Les écosystèmes forestiers constituent le principal réservoir à long terme de carbone. Toutefois, les dynamiques saisonnières de productions de cette biomasse ligneuse, en relation avec l'assimilation du carbone par l'écosystème et les déterminants environnementaux, restent peu étudiées, limitant notre compréhension du cycle du carbone et particulièrement sa sensibilité aux changements actuels du climat. Cette thèse a pour objectif de comprendre les relations entre le processus de séquestration du carbone dans le bois en formation, la physiologie de l’arbre, l’assimilation du carbone par le peuplement, et les conditions environnementales du site. L’étude porte sur trois sites instrumentés d’une tour à flux avec un peuplement constitué principalement par, respectivement l’épicéa à Tharandt en 2016, le hêtre à Hesse en 2015-2017, et le chêne à Barbeau en 2016. La formation du bois a été suivis par prélèvement hebdomadaire de microcarottes contenant, le phloème, le cambium et le xylème en formation sur des arbres dominants sélectionnés dans l’empreinte de mesure de la tour. La productivité primaire brute a été estimée par Eddy-Covariance, et les variables climatiques mesurés grâce aux dispositifs de la tour. En premier, nous avons mis au point une nouvelle approche histologique, plus rapide et plus précise que la méthode précédemment publiée sur les résineux, pour quantifier la dynamique intra-annuelle de la séquestration du carbone dans le bois en formation, basée sur des mesures répétées de la densité apparente du xylème, et applicable également aux angiospermes. Dans le 2nd chapitre, nous avons montré que l’occurrence en même temps du développement de la canopée et de la reprise de l’activité cambiale pouvait ralentir la croissance radiale du xylème, et favoriser la formation d’un xylème à porosité élevée mais rapidement fonctionnel. Dans le 3ème chapitre, nous avons démontré que le plan ligneux détermine la coordination temporelle entre la croissance en taille et en biomasse du tronc au cours de la saison de végétation, la séquestration du carbone dans le bois en formation étant toujours décalée derrière la croissance radiale du tronc due aux processus internes de la xylogenèse, avec une tendance croissance du décalage temporel pour l’épicéa et le hêtre, mais une tendance décroissante chez le chêne. Le 4ème chapitre démontre que indépendamment du peuplement, la dynamique d'assimilation du carbone présentait une courbe en cloche symétrique culminant en Juin, tandis que la dynamique saisonnière de la séquestration du carbone variait entre les 3 espèces. Le peuplement de hêtres a concentré la séquestration du carbone dans le tronc en Mai-Juillet, tandis que les peuplements d'épicéa et de chênes ont plutôt culminé en Juin-Août et ont concentré cette séquestration vers la 2ème partie de la saison de végétation. Dans le 5ème chapitre, grâce à un suivi de trois ans des flux de carbone, de la croissance des arbres, et des facteurs environnementaux dans le peuplement de hêtres matures, nous avons montré que le classement du bilan de carbone annuel n'était pas maintenu d'une année à l'autre, avec l’assimilation de carbone annuel la plus élevée en 2017, mais la production de biomasse ligneuse la plus élevée en 2016. Cela suggère que l'allocation du carbone de l'assimilation à la séquestration dans la tige ne suit pas une simple règle d’allométrie. Enfin, nous avons observé que, parallèlement à la formation d'un nouveau xylème, la teneur en amidon augmentait également durant la formation du bois. Cela suggère que le stockage de carbone et la croissance du tronc étaient étroitement liés, avec une proportion plus importante chez le chêne que chez l’épicéa et le hêtre. Ainsi, cette thèse a permis d'améliorer nos connaissances sur la dynamique de l'allocation du carbone dans l'arbre, de l'assimilation au niveau des feuilles à la séquestration à long terme dans le bois, et d'explorer leur sensibilité respective aux conditions climatiques. / Forest ecosystems are the major and most perennial terrestrial carbon pool. However, the seasonal dynamics of production of this woody biomass, in relation to the ecosystem carbon uptake remain poorly studied, limiting our understanding of the carbon cycle and particularly its sensitivity to current climate changes. This thesis aimed to better understand the underlying process of carbon sequestration within forming wood, as related to tree physiology, stand carbon assimilation and site environmental conditions. The study was conducted on three instrumented site with a flux tower, the stand is dominated respectively by spruce in Tharandt in 2016, by beech in Hesse in 2015-2017, and by oak in Barbeau in 2016. To monitor wood formation, wood samples containing phloem, cambial zone, and developing xylem were collected weekly on dominant trees within the tower footprint. Flux tower measurements were used to estimate the daily GPP of the stand, and record the climatic conditions. In the 1st chapter, we developed a novel histologic approach, to quantify the intra-annual dynamics of carbon sequestration in spruce forming wood. This approach, based on repeated measurements of xylem apparent density, is easier, faster, and more accurate than the previously available method, and is applicable also to angiosperm species. In the 2nd chapter, we showed that simultaneous occurrence of the canopy development and the resumption of cambial activity slowed down xylem radial growth, and might entail the formation of xylem with high porosity but functional at early growing season. In the 3rd chapter, we demonstrated that the tree-ring structure determined the temporal coordination between stem growth in size and in biomass along the growing season, with carbon sequestration in forming wood always lagging behind stem radial growth due to inner processes of xylogenesis. Indeed, we showed an increasing timelag ranging from ten days to nearly one month for spruce and beech, but a decreasing timelag from nearly three to one week for oak trees. In the 4th chapter, we observed that regardless of the stand, carbon assimilation followed a large and symmetric bell curve peaking in June, while seasonal dynamics of carbon sequestration differed among the three species. The beech trees concentrated carbon sequestration in stem in May-July, while the spruce and oak trees rather peaked in June-August, and completed stem growth towards the second part of the growing season. In the 5th chapter, based on a three-year monitoring of carbon fluxes, trees growth and environmental factors in the mature beech stand, we showed that ranking of annual carbon balance was not maintained from one year to another, with higher carbon assimilation during the hottest year, but higher woody biomass production in the wettest year. This suggests that allocation of carbon from assimilation to sequestration in stem is not following a simple allometric rule. In the last chapter, we observed that parallel to formation of a new xylem, starch content also increased in forming wood, suggesting that storage and stem growth were tightly connected along the growing season, with higher allocation to storage for sessile oak, compared to spruce and beech. This thesis has improved our knowledge about the dynamics of carbon allocation in the tree, from assimilation at the leaf level to long-term sequestration into the wood, and allowed to explore their respective sensitivity to climate conditions. A better quantification of the shift between stem growth in size and in biomass will require to disentangle the kinetics of cellulose and lignin deposition. However, our work contributed to a better understanding of the intra-annual dynamics of stem radial growth and carbon sequestration, which could help to improve modelling of forests net primary productivity, in the context of current global warming.

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Urbana parker är en central del i människors välbefinnande. De är platser för rekreation, aktiviteter och sociala utbyten. Forskning visar att undervinterhalvåret minskar användandet av parker i tempererade klimat vilket kan medföra negativa hälsoeffekter för människor. Att parker står obrukade delar av året är negativt både utifrån ett socialt- och resursperspektiv. Syftet med följande arbete är att undersöka hur kvartersparker kan anpassas för att öka användningen året runt. Målet är sedan att presentera en visualisering av förbättringsförslaget för Stenebergsparken i Gävle. En variation av metoder användes för att genomföra arbetet, där samtliga grundar sig i tidigare vetenskapliga publikationer. Platsanalys, webbenkät, intervjuer och en solstudie är de metoder som användes för att besvara studiens frågeställningar. Utifrån resultaten av dessa gestaltades ett förbättringsförslag somvisualiserades med renderingar och en video. Under arbetets gång framkom tre koncept som anpassning av parker i tempererade klimat bör utgå ifrån vid förändring, mikroklimat, aktivitet och utformning. Mikroklimat innebär att skapa behagliga klimat som erbjuder vistelse i olika typer av önskade väderförhållanden. Exempelvis möjligheten till sol- och skuggytor samt skydd mot nederbörd och vind. Utifrån aktivitet behöver parker erbjuda en variation av sysselsättningar för att kunna tillgodose flera behov. Denna aktivering innebär att en större mängd människor lockas till platsen. Utformning handlar om att tillgängliggöra ytor samt placera aktiviteter utifrån olika mikroklimat i parker. För att validera förbättringsförslaget presenterades det till två objektiva sakkunniga inom arkitektur och landskapsarkitektur. Följande studie visar på att vid utformning av kvartersparker i tempererade klimat behöver de tre koncepten mikroklimat, aktivitet och utformning tas i beaktning. Omplanerare, kommuner och politiker ser till dessa tre koncept ger de människor förutsättningar för att bruka parker under hela året i större utsträckning. / Urban parks are important components of people’s well-being and everyday life. These parks are a place for recreation, activities and social encounters.Previous research show that during the colder seasons the use of parks in temperate climates decreases, which in turn can have a negative outcome on people’s general health. The fact that urban parks are unused for a considerable part of the year is negative from both a social- and resource perspective. Therefore, the aim of this study is to investigate how neighborhood parks in temperate climates can be adapted to increase use all year round. Following the objective to present a visualization of the presented proposal for the case study of Stenebergsparken in Gävle. A combination of different methods was used and all methods were based on previous research. Site analysis, web survey, interviews and a solar study are the selected methods used to help answer the study's research questions. Throughout the process three concepts regarding adjustments of parks in temperate climates emerged, these were microclimate, activity and design. These concepts are essential to be taken in consideration during the planning process to create lively parks year around. Microclimates means to create pleasant environmentsthat enables visits in different types of desired weather conditions. This can be achieved through creating places that provide both sun and shade or creation of protection against precipitation. For activity parks need to offer a variety ofactivities to satisfy multiple interests. In turn, this attracts a greater number of visitors to the place. The design of a park involves the availability of the park and placement of activity surfaces regarding microclimate aspects. To validate the proposed improvements renderings together with a checklist was presented to two unbiased experts in architecture and landscape architecture.The produced proposal in this case study, regarding seasonal adjustment of neighborhood parks in tempered climates, is based upon the three emerging concepts microclimate, activity and design. If planners, municipalities and politicians look to these three concepts, they enable people to use parks throughout the year to a greater extent.

The variation in community composition among sites is often used to gain insight into the processes of plant community assembly. In this study, we looked for evidence of environmentally and spatially mediated community assembly mechanisms in a temperate forest in eastern North America. To test this, we measured, identified and mapped all woody stems ≥1 cm in diameter at breast height (DBH) in 12 ha of a 20 ha forest plot. We used principal coordinates of neighbor matrices (PCNM) to obtain variables that modelled spatial processes (eg. dispersal, drift) at the community level. Topographic variables (slope, elevation, convexity, aspect) were used to model environmental conditions. Variation partitioning was used to isolate the unique and shared effects of topographic and spatial variables on community composition. We were also interested in studying how associations with the environment change with tree size. For this we assessed the abundance of a subset of focal species in response to topography as well as human disturbance. Species abundance were divided into three stem size classes: small (< 5 cm), medium (≥5 cm and < 15), and big (≥15 cm). We found that topography and space jointly explained 63% of the variation in community composition. This variation was almost entirely spatially structured with the component of pure topography only contributing 1% to the total explained variation. A redundancy analysis showed that slope and elevation were the most important topographic variables structuring the distribution of trees. The focal species had largely independent distributions across the environmental gradients and three of the five species showed within-species differences associated with size class effects on the relationship with topography and human disturbance. The implications of these results are relevant to conservation efforts and suggest that large contiguous areas of heterogeneous environments are essential in maintaining biodiversity. / Thesis / Master of Science (MSc)

In the temperate region, bats have evolved the strategy of hibernation to survive the harsh winter. During hibernation, bats enter the vulnerable state of torpor that requires specific environmental conditions to function optimally. Bats are known to use caves and anthropogenic structures as hibernation sites. However, the majority of the bat population cannot be accounted for when such structures are surveyed. There is evidence that bats use other natural structures as hibernation sites. To examine bat’s choices of hibernation sites and activity, acoustic monitoring of bats in south-west Sweden was performed during the winter of 2022-2023. Bat activity was measured in areas with potential hibernation sites in natural structures (rock outcrops), as well as inside and outside of known hibernation sites (anthropogenic structures). The level of activity and the ambient temperature were tested for a possible correlation. Additionally, data from 2006-2022 of surveys of bats in hibernation sites were examined for a possible relationship with outside ambient temperature. Bats were found to be active during the winter inside the known sites of hibernation. There was also activity recorded outside one of the known hibernation sites, but no bat activity was found in the areas of potential hibernation sites. No significant correlation was shown between bat activity and outside temperature, nor between number of bats inside a hibernation site and outside temperature. Further research is needed to develop the knowledge about bats’ hibernation behavior which in turn will aid more effective conservation of temperate bat species.

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<p>Continuous measurements of carbon fluxes and meteorological variables were made at a newly initiated flux tower site at an oak-dominant temperate deciduous forest in Southern Ontario, Canada from January to December 2012. Results indicate this forest was a moderate carbon sink in 2012. Annual values of net ecosystem productivity (NEP), gross ecosystem productivity (GEP) and ecosystem respiration (R) were 263 ± 30, 1192 and 922 g C m^-2, respectively. An unusual warm period in March caused a strong increase in R. Erratic peaks of daily air temperature in April also increased R. A drought in July and early August reduced NEP rates when soil moisture values reached the lowest point of the year in late July and early August (minimum 0.023 m³ m^-3). This decrease in NEP was mostly caused by a decrease in GEP, rather than increased R. Water use efficiency at this deciduous forest was 2.86 g C kg^-1 H₂O, indicating conservative water use by the forest. Downwelling photosynthetic active radiation (PAR) was a dominant environmental control on photosynthesis, followed by air temperature and vapour pressure deficit, except in extreme dry periods when soil water stress affected carbon uptake. Extremely cloudy days in the growing season resulted in net carbon release due to low photosynthetic uptake values. Results indicate that large climatic fluctuations in this region may cause high instability in photosynthetic carbon uptake and release from soil carbon pools. This study helps to evaluate and quantify the responses of deciduous forests in the Great Lakes region to future climate change and extreme weather events.</p> / Master of Science (MSc)

Total organic carbon (TOC) is a critical parameter when investigating the health of aquatic ecosystems. This report details the findings of the study on fluctuations of TOC concentration in Fylleån catchment are between January 2001 and December 2023 (23-year period). The study provided valuable insights into the long-term trends in TOC concentrations and its association with changes in river water discharge and surface water temperatures. The study revealed significant spatial and temporal variations, with higher TOC levels in areas with intensive anthropogenic activities (downstream), and lower levels in forested regions (upstream). Temporally, TOC concentrations exhibit distinct seasonal patterns, peaking in late autumn and early winter due to increased organic runoff and decreasing in late spring and summer due to reduced precipitation and higher biological activity. Online datasets were downloaded to aid in the assessment of the presence of a seasonal trend in changes in riverine TOC concentration. The same dataset was used to calculate the correlation between seasonal TOC concentration and river discharge / surface water temperature. Upstream TOC concentration ranges were 5.5-13.97mg/l in winter, 5.97-11.07mg/l in spring, 8.63-20.37mg/l in summer and 7.07-20.73mg/l in autumn. Downstream TOC concentration ranges were 6.83-19.07mg/l in winter, 6.43-12.83mg/l in spring, 6.33-16.97mg/l in summer and 6.23-24.53mg/l in autumn. For all the three stations, standard deviation was lowest in spring (1.39, 1.58, &amp; 1.45) and highest in autumn (4.09, 3.06, &amp; 3.59) at Fylleån-fyllebro, Trönningeån-trönninge, and Lillån Ga Järnvägsbron respectively. There was a positive correlation between TOC concentrations and river discharge. Results for correlation between surface water temperature and seasonal TOC concentration were generally positive with only summers showing purely negative correlation. The study concluded that there are seasonal trends in TOC concentrations which are partly influenced by river discharge and surface water temperatures.

Among the most compelling and least well-understood tree species growing in the temperate forests of southern South America is Fitzroya cupressoides, a high biomass species and the second longest-lived tree species in the world. This thesis quantified the main components of the carbon cycle in Fitzroya forests (i.e. net primary productivity (NPP) and soil respiration) and evaluated the environmental variables that are most related to them. The study was focused on medium-age and old-growth forests growing in the Coastal Range (Alerce Costero National Park, AC) and the Andean Cordillera (Alerce Andino National Park, AA) of southern Chile, respectively. The specific objectives of this thesis were to: 1) assess the forest structure, species composition and characterise the environmental conditions of these forests; 2) assess biomass, aboveground NPP, carbon allocation and mean wood residence time in these forests; 3) assess soil respiration and relate it to soil environmental conditions. Additionally, to use a mass balance approach to estimate fine root productivity; 4) estimate total NPP using biometric and indirect estimates of productivity; 5) evaluate the climatic factors mainly related to Fitzroya stem radial change on an intra-annual basis; and 6) evaluate changes in Fitzroya's tree growth and carbon isotopes during recent decades, and determine which environmental factors are more related to them. The last two objectives focus on Fitzroya as the dominant species and the subject of this study. Two 0.6 ha plots were installed within each national park; NPP was estimated for a year and soil respiration and high resolution stem growth measurements were monitored over almost two years. Aboveground biomass estimates for the Andean site are among the most massive reported in the world and carbon fluxes in Fitzroya forests are among the lowest reported for temperate wet forests worldwide. The longevity as well as the particularly rainy and nutrient poor soil conditions where these ecosystems grow may influence their exceptionally slow carbon dynamics. Differences in carbon fluxes between sites seem most probably driven by different environmental conditions rather than by developmental stage. Moreover, carbon fluxes were more sensitive to interannual climate variability in AC than AA. Warmer and drier summer conditions, likely to become more common under future climate change, more significantly affected stem growth and soil respiration in the Coastal Range than in the Andes. Regarding long-term changes, tree growth has been decreasing in the coastal site in the last 40 years and increasing in the Andes since the 1900s. These trends have been accompanied by an increase in intrinsic water use efficiency which is likely caused by rises in CO₂ and changes in climate conditions in both sites. Although Fitzroya grows in particularly wet and cool areas, projected drier and warmer conditions may have a negative effect on Fitzroya stem growth and carbon sequestration in both study sites. This effect would be more critical in the Coastal Range though, because of its more Mediterranean climate influence and more restrictive soil conditions in this area. Adequate resources are needed for the monitoring and conservation of these slow growth and massive forests especially in the Coastal Range, in order to avoid ongoing illegal cuttings and threatening forest fires.