Sustainable forest management practices are crucial for minimizing environmental impacts, and to keep forests and the underlying soils healthy to maintain productivity, and to improve adaptability to climate change and mitigate it in the long-term. There, carbon and nitrogen cycling play crucial roles in proper functioning of forest ecosystems.
The overall aim of this thesis was to explore the effects of logging residues on the early-stage dynamics of the main nitrogen and carbon cycling processes in upland forest soils after final felling. A specific aim was to compare the effects of logging residue piles consisting of different tree species, i.e., Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and silver birch (Betula pendula Roth). A special attention was given to the response of soil to different amounts of residues.
The effect of logging residues on soil chemical properties and processes was stronger in the organic layer than in the mineral soil layer. Logging residue piles stimulated carbon and nitrogen cycling, especially net nitrification within the first year after the residue treatment. Subsequently, nitrogen was lost via leaching as nitrate and gaseous emission as nitrous oxide. Nitrous oxide fluxes were generally low, although higher in the plots containing logging residues. Spruce residues tended to stimulate nitrous oxide emissions for longer than the residues of the other tree species. Depending on the tree species, nitrous oxide production originated from both autotrophic nitrification and denitrification. Nitrogen concentrations in the soil percolate water already accelerated one year after the establishment of the residue piles. Logging residues increased nitrate and ammonium concentrations, which were highest under birch residues. The effect of logging residue piles on soil was stronger when compared to milder tree species effects. Biological nitrogen fixation activity tended to be higher in branches than in needles or leaves, and higher in coniferous residues.
The results of this study raise the importance of more even distribution of logging residues on the forest floor instead of piling them to avoid harmful environmental effects and to maintain soil nutrient balance. The ability of soils to retain nitrogen needs additional attention in forest management practices, especially in boreal areas where nitrogen limits the growth of forests.
Boreal forest soils are globally one of the most extensive carbon storages, whereas soil respiration (CO2 efflux) forms the largest carbon flux from the ecosystem to the atmosphere. Current changes in the world climate may have unpredictable effects on belowground carbon processes, and thereby, on the carbon balance of boreal forests.
To better understand the various processes in soil and to quantify the potential changes in the carbon cycle, forest-floor respiration (RFF) was partitioned into five different components, and tree-root respiration (RR) was estimated, using four different methods in a mature boreal Scots pine (Pinus sylvestris L.) stand in southern Finland. Non-structural carbohydrate (NSC) concentrations in tree roots were determined, and carbon allocation to belowground by trees was estimated with the whole-tree carbon model ‘CASSIA’. In addition, RR and heterotrophic soil respiration (RH) were separated using root exclusion in seven coniferous forests along a latitudinal gradient in Northern and Central Europe.
The RR comprised almost half of the RFF, the RH almost a third, and ground vegetation and respiration of mycorrhizal hyphae the remaining fifth in the boreal Scots pine stand. While the annual RR decreased throughout the first three study years, the RH increased when the mycorrhizal roots were excluded from the treatments. The RR and most of the NSC concentrations were higher in the warmer years and lower in the cooler, as estimated with most of the methods. Three methods resulted in rather similar RR estimations, while the RR estimated with root incubation was significantly lower. The RR was over 50% of the annual photosynthesis in the northernmost forest stand, whereas in the southernmost stand it was only up to 15%. Carbon allocation to the belowground, as modelled with CASSIA was a third of the annual photosynthesis on average and almost 5% for the symbiotic mycorrhizae.
This study aims to 1) quantify the spatial and temporal variation in diffusive and ebullitive methane fluxes, and to 2) assess the quantity and quality of BVOC emissions and how they are controlled by vegetation composition and environmental factors in boreal peatlands.
Methane fluxes were measured with static chambers and bubble traps from a boreal ombrotrophic bog and compared to eddy covariance measurements on the ecosystem level. BVOC emissions were measured with dynamic chambers from the same boreal bog and a nearby boreal fen. Vegetation removal treatments were applied to differentiate BVOC emissions from intact vegetation, mosses, and peat.
Both methane and BVOC emissions showed strong seasonality linked to temperature and vegetation phenology. While diffusive methane fluxes did not differ between three years or different plant community types, methane ebullition was highest during the wettest of the three years studied and varied spatially being greater from open water pools than from wet bare peat surfaces. Decrease in water table led to higher ebullition, but so did also increase in air pressure. In total, ebullition contributed only 2 % – 8 % to the methane emission on the ecosystem level, which supports the general paradigm that diffusion through peat and aerenchymatous plants are the main pathways for methane from peat to the atmosphere.
Isoprene was the most emitted BVOC from both peatlands. Isoprene emission was strongly linked to sedges, and thus isoprene and total BVOC emission rates were higher in the sedge-dominated fen than the shrub-dominated bog. Moreover, total BVOC and isoprene emissions were highest from intact vegetation. However, organic halide emissions had stronger link with water level as they were absent during exceptional drought in the summer 2018. Therefore, warming climate and associated drougths and shrubification are likely to alter the quality and quantity of BVOCs emitted from boreal peatlands.
In Finland, peatland forests are significant for wood supply, although simultaneously, they are also important for biodiversity, carbon sequestration, water conservation, and recreation. In the 1960s and 1970s, peatland forests in Finland were extensively drained to increase tree growth and fulfil the needs of the forest sector. However, this extensive drainage has negatively impacted on the biodiversity of peatland ecosystems, and substantially increased nutrient and sediment emissions to lakes and rivers resulting in eutrophication, turbidity, and brownification of these water bodies.
This dissertation presents a number of approaches to move peatland forest management in a more environmentally sound direction, which may increase the general acceptability of peatland forestry. Airborne LiDAR (Light detection and ranging, i.e., laser scanning) derived 3D point cloud provides useful data, for example, to estimate forest biomass, to identify low-productive peatland forests, to model overland water flows, and to identify wet areas. The strength of airborne LiDAR is the ability of laser pulses to pass through tree canopies and obtain accurate observations from the ground level. The information derived from airborne LiDAR can enhance the planning of peatland forest management, as much of the planning can be done remotely, and supplementary field work can be implemented in areas of strategic need.
This study presented the novel idea of applying local binary patterns for the prediction of terrain trafficability, which should be considered in further studies and practice. The moisture index derived from the local neighborhood can reveal the small-scale variations in terrain moisture. This study also presented the novel idea to create spatial models to identify suitable locations for water protection structures, which may help forest managers to plan water protection of ditch network maintenance or peatland restoration operations. Overall, the utilization of airborne LiDAR-derived information for the development of peatland forestry practices shows great potential.
Boreal forests assimilate a substantial fraction of global atmospheric CO2 and thus play a key role in the global carbon cycle. However, due to the prevalence of evergreen species, monitoring photosynthetic dynamics of boreal forests is challenging when using conventional greenness- or vegetation-indices. Fortunately, an increasing body of evidence suggests that chlorophyll-a fluorescence (ChlF) – a weak red-to-far-red radiation emitted by the chlorophyll a molecules nanoseconds after light absorption – can enhance our capacity to assess photosynthetic dynamics in evergreen-dominated ecosystems. However, before extracting complete information embedded in the ChlF, comprehensive understanding and quantitative characterization of the mechanisms that connect the measured ChlF to photosynthesis across various scales are essential.
In this thesis, I discuss several challenges that we currently need to face to leverage the full potential of ChlF. I present a roadmap through these challenges, towards a more comprehensive interpretation of ChlF. The main focus is laid on the challenges concerning ChlF measured at a leaf-level in methodological and mechanistic contexts. In other words, this thesis contributes to the interpretation of ChlF by contextualizing the influence that methodological and mechanistic factors have on leaf-level spectral ChlF.
An impact of methodological factors, measuring geometry and sample arrangements, on spectral ChlF was analysed. Results indicate that ChlF shape is less dependent on measuring geometry as compared to ChlF magnitude and that if needle-mats are used, measuring geometry does not lower the comparability between studies using different setups. Mechanical factors were investigated in terms of their effect on spatial and temporal variation in spectral ChlF. The diversity of species and light environments within an ecosystem was shown to generate a temporarily-invariant, baseline variation in leaf spectral ChlF, as well as contrasting seasonal photosynthetic acclimation patterns. Consequently, I suggest the need for considering both the methodological and mechanistic contexts in the interpretation of ChlF.
Forests are dynamic ecosystems that are constantly changing. The most common natural reasons for change in forests are the growth and death of trees, as well as the damage occurring to them. Tree growth appears as an increment of its structural dimensions, such as stem diameter, height, and crown volume, which all affect the structure of a tree. Repeated measurements of tree characteristics enable observations of the respective increments indicating tree growth. According to current knowledge, the tree growth process follows the priority theory, where trees aim to achieve sufficient lightning conditions for the tree crown through primary growth, whereas increment in diameter results from the secondary growth. Tree growth is known to have an effect on the carbon sequestration potential of trees as well as on the quality of timber. To improve the understanding of the underlying cause–effect relations driving tree growth, methods to quantify structural changes in trees and forests are needed.
The use of terrestrial laser scanning (TLS) has emerged during the recent decade as an effective tool to determine attributes of individual trees. However, the capacity of TLS point cloud-based methods to measure tree growth remains unexplored. This thesis aimed at developing new methods to measure tree growth in boreal forest conditions by utilizing two-date TLS point clouds. The point clouds were also used to investigate how trees allocate their growth and how the stem form of trees develops, to deepen the understanding of tree growth processes under different conditions and over the life cycle of a tree. The capability of the developed methods was examined during a five- to nine-year monitoring period with two separate datasets consisting of 1315 trees in total.
Study I demonstrated the feasibility of TLS point clouds for measuring tree growth in boreal forests. In studies II and III, an automated point cloud-based method was further developed and tested for measuring tree growth. The used method could detect trees from two-date point clouds, with the detected trees representing 84.5% of total basal area. In general, statistically significant changes in the examined attributes, such as diameter at breast height, tree height, stem volume, and logwood volume, were detected during the monitoring periods. Tree growth and stem volume allocation seemed to be more similar for trees growing in similar structural conditions.
The findings obtained in this thesis demonstrate the capabilities of repeatedly acquired TLS point clouds to be used for measuring the growth of trees and for characterizing the structural changes in forests. This thesis showed that TLS point cloud-based methods can be used for enhancing the knowledge of how trees allocate their growth, and thus help discover the underlying reasons for processes driving changes in forests, which could generate benefits for ecological or silvicultural applications where information on tree growth and forest structural changes is needed.
The era of airborne laser scanning (ALS) and the development of new forest inventory methods has reduced the need for field visits and overall inventory costs over the last two decades. Although the development of inventory methods has been considerable, some systematic field visits are usually always required. For example, the most common ALS inventory method, the area-based approach (ABA), leans on field sample plot measurements. Likewise in the ALS inventory, the ABA method can also be used in drone-based inventories with image point cloud (IPC) data. Due to the small areal coverage of the drones, local sample plot measurements in drone image point cloud (DIPC) inventories are not usually profitable. The objective of this thesis was to examine the performance of ALS-based forest attribute models in ALS- and DIPC-based ABA inventories without new in-situ field measurements.
In this study, nationwide ALS models for three forest attributes (stem volume, above ground biomass and dominant height) were fitted for the whole of Finland, and regional-level error rates of the nationwide model predictions were assessed. As the nationwide models tended to exhibit systematic region-wise under- and over-predictions, different calibration methods were examined. First, calibration of nationwide models with a small number of new field measurements from the target area was simulated. Second, the nationwide stem volume model or its regional predictions was calibrated without new in-situ field measurements by three test scenarios: a) using additional calibration variables in the models to account for geographical and environmental conditions throughout the country, b) refitting of the models by using existing sample plots from nearby regions, and c) matching the regional-level predictions with national forest inventory data. The DICP-based forest inventory without new in-situ field measurements was evaluated by replacing the ALS metrics from the ALS-based models with DIPC metrics when the models were applied. In the DIPC inventory, the metrics used in the ALS models were selected carefully so that they would be similar to the corresponding DIPC metrics.
The results showed that forest attributes can be predicted without new in-situ field measurements using nationwide ALS-based models with moderate error rates. The systematic errors associated with the nationwide models decreased when the models were fitted with additional calibration variables, such as degree days, precipitation, and tree species proportions. However, the measurement of a carefully selected set of sample plots (e.g., 20 plots) from the target area for the calibration of the nationwide model is recommended, in instances where it is economically feasible. Prediction of forest attributes using ALS-based models with DIPC metrics is possible provided the predictor variables describe the upper canopy layer. The lowest error rates in DIPC-based inventories were obtained when the ALS-based model was fitted in a nearby region and the inventory units were disaggregated to coniferous and deciduous dominated areas before the prediction.
In Finland, there is a desire to extend the planting season from spring and early summer to autumn, and to use the closed cardboard box storage method for both dormant and non-dormant seedlings. This thesis examined the effects of planting practices and the growing environment on the early performance of boreal container seedlings, and specifically: i) What are safe durations for the field storage of non-dormant Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) seedlings in closed cardboard boxes and open tray storage for different planting seasons (I); ii) How planting success differs in one-year-old spring, summer, and autumn plantings of Norway spruce and Scots pine in practical forestry (II); iii) How the planting depth and/or planting season affect the early field performance of small-sized silver birch (Betula pendula Roth) and Scots pine container seedlings (III) and iv) How warmer growing conditions affect the growth and emissions of biogenic volatile organic compounds in boreal seedlings in a controlled field experiment (IV). Non-dormant conifer seedlings can be stored in closed boxes for three days in August and a week in May, September, and October, whereas for open-stored seedlings the duration is a couple of days longer (I). Norway spruce plantings can be successful from spring to autumn if seedling storage, duration, and planting instructions are followed carefully. In Scots pine, it is still recommended to plant seedlings only in spring and early summer due to the higher failure risk (II). Deeper planting (60-80 % of shoot underground) may also enhance the early field performance of small-sized seedlings (III). Silver birch might benefit more from climate warming compared to conifer seedlings (IV). To ensure forest regeneration success with boreal tree species, recommendations for seedling materials, storage, and planting practices in different planting seasons should be carefully followed.
Information on timber assortment recovery and wood quality is crucial for wood procurement planning, as the various tree species and wood dimensions and qualities may be utilized and refined in separate mills. The aim of this thesis is to improve our understanding of the timber trade in digital environments in order to support the planning of harvesting operations.
The work for the thesis was carried out in three areas, two of which (discussed in Papers I and II) were located in Eastern Finland and one (Paper III) in Southern Finland. The field data comprised tree characteristics obtained from 79, 99 and 665 sample plots (Papers I, II and III, respectively), 249 harvested stands (Paper III) and a stem quality database (Papers I and III), whereas the remote sensing material consisted of aerial imagery (Papers I and III) and airborne laser scanning (ALS) data (Papers I, II and III) covering all the sites.
With the stated overarching aim, we set out in Papers I and III to estimate timber assortment volumes, economic values and wood paying capabilities (WPC) for plots (Paper I) or stands (Paper III) with different bucking scenarios, and used the resulting timber assortment estimates to assess logging recoveries. The alternative bucking scenarios investigated were (1) bucking-to-value using maximum sawlog and pulpwood volumes but excluding quality (theoretical maximum), and (2) bucking-to-value using sawlog lengths at 30 cm intervals for Scots pine (Pinus sylvestris L., Papers I and III) and Norway spruce (Picea abies (L.) H.Karst, Paper III) and veneer logs of lengths 4.7 m, 5.0 m, 6.0 m and 6.7 m for birch (Betula spp., Paper III), either excluding or including wood quality indicators. The first approach resembled the state-of-the-art in Nordic forestry business circles and the second approach went beyond that. The commercial value of timber stands is substantially affected by the quantity of understorey trees, and pre-harvest clearing is typically needed when forest stands have an understorey vegetation that hinders harvesting operations. We therefore proposed a method in Paper II for estimating this need for the pre-harvest clearing of small trees (diameters at breast height < 7 cm).
The results showed that use of the methods developed in this thesis could support wood procurement practices by (1) locating valuable stands with the desired timber assortment distributions (Papers I and III), (2) identifying understorey vegetation that needs to be removed before harvesting (Paper II), and (3) reducing costs, as the number of field visits needed before harvesting will diminish (Papers I, II and III).
In conclusion, the present findings may make timber markets more competent, since the methods developed here provide detailed pre-harvest information that can be used as a decision support tool by either buyers or sellers of timber in traditional and digital marketplaces.
For the past 25 years, the Finnish state has supported the diffusion of wooden multistory construction into the construction sector. Given the socio-cultural and economic value of Finland’s forest sector, there is precedent to do so. Nonetheless, wooden multistory construction remains a niche construction practice in its formative phase. This dissertation researches the diffusion of wooden multistory construction by analyzing perceptions from municipal civil servants tasked with overseeing land use planning in Finland. Despite being gatekeepers of local construction activities, their perceptions towards wooden multistory construction are understudied. To access these perceptions, this research applies the theory of planned behavior. At the root of this theory lies the notion that beliefs underpin human action. Specifically, this dissertation research identifies (Article I) and operationalizes (Article II-III) the attitudes and beliefs that municipal civil servants hold towards wooden multistory construction. The results are distilled into three empirical accounts. Why not wood? (Article I) reframes elicited beliefs as barriers and benefits to wooden multistory construction. Benefits include a variety of holistic topics ranging from improving the lifestyles of citizens and supporting local wood-based businesses, to facilitating aspects of building construction. On the other hand, multiple barriers coalesce to form a risky and costly environment that results in project aversion. Wood versus concrete (Article II) analyzes how outcomes of implementing wooden multistory buildings are relativized against concrete multistory buildings. In large part, wooden multistory buildings are believed to possess several superior qualities (e.g., environmental performance, economic development outcomes). Nevertheless, apprehensions persist (e.g., they are more expensive to build and maintain, they are more susceptible to fire). Background experiences, especially occupational profession, play a key role in shaping several beliefs. Planning for wood (Article III) studies the relationship between how beliefs (i.e., environmental performance, economic development, cost-related attributes, technical qualities) form attitudes towards wooden multistory buildings. The prioritizations of beliefs vary according to occupational profession. Planning practitioners form attitudes holistically, based on the building’s environmental performance, technical qualities, and economic development outcomes. Other administrators form attitudes primarily based on the project’s economic development outcomes and technical qualities. Ultimately, municipal civil servants appear receptive towards implementing wooden multistory buildings in their municipalities, but this receptiveness hinges on project outcomes and the “societal goods” prioritized by the individual respondent. Even if wooden multistory buildings are perceived to possess superior qualities (e.g., environmental performance), these qualities may not strongly impact an individual’s attitude towards favoring the project. Different prioritizations among municipal civil servants might lead to planning tensions within the municipal administration, but it remains to be seen how these tensions enable (or hinder) wooden multistory construction diffusion.
The utilization of forest side-streams is associated with the applied bioenergy technology that must be impellent to support the increasing demand for biofuels and resources while lowering greenhouse gas (GHG) emission from the transport sector. This study aimed to estimate potential biofuel production from eutrophic (EL) and mesotrophic (ML) lake bottom biomass and the manufacturing side-streams from the pulp and paper mill (PI – PVIII). Theoretical biogas and bioethanol productions were modeled by Aspen Plus® simulation through 1) saccharification and fermentation, 2) gasification and mixed alcohol synthesis, 3) gasification-syngas fermentation, and (4) anaerobic digestion processes. In addition, the different process stages of the pulp and paper side-streams was studied by ABE fermentation using Clostridium acetobutylicum DSM 1731.
The bioethanol produced from EL and ML biomass from indirect gasification and mixed alcohol synthesis were 244.5 L/t and 57.1 L/t, whereas the yields from saccharification and fermentation were 137 L/t and 40 L/t, respectively. The EL biomass produced the most profitable bioethanol production from the latter process. The ML and EL biomass produced biogas of 38.9 mL/g volatile solid and 136.6 mL/g volatile solid, respectively. The ash from the EL and ML biomass and the dried samples of PI and PIII could be used as fertilizer because the harmful elements for Finnish fertilizer products were below the detectable limit. The primary sludge (PII) sample had found high N and P concentrations and cadmium (Cd) concentration (3 mg/kg), which exceeded the Cd limit for Finnish fertilizer products (1.5 mg/kg). However, wet primary sludge (PII) forming 300,000 tonnes/year (72600 dry tonnes) produced anhydrous ethanol about 3011 kg/h (24,090 tonnes/year) when PII was used for the gasification-syngas fermentation process in the bioethanol plant model.
Three pulp and paper side-streams (PI, PII and PIII) with unwashing and water washing were pretreated with dilute acid (0.2% H2SO4 at 180 °C for 10 min), followed by saccharification and ABE fermentation. The results suggested that water washing did not affect the PII and PIII prehydrolysate sugar recovery, as well as enzyme hydrolysis of the rejects from kraft pulping (PI) did not require prewashing before dilute acid pretreatment. In addition, the unwashed PI side-stream yielded the highest ABE concentration of 12.8 g/L, compared to the unwashed PII and PIII side-streams, 5.2 g/L, and 6.3 g/L, respectively. The side-streams from different process stages in pulp and paper mill were concluded to be high potential feedstocks for biofuels production due to their chemical compositions. The unwashed PI was suitable feedstock for butanol production, while PII could be fully utilized in the integrated gasification-syngas fermentation process. Primary sludge (PII) was found to be a promising feedstock for bioethanol and an internal rate of return (IRR) of 15 % can be obtained by two implementations. One was a cost-competitive ethanol selling price (ESP) of €0.61–0.71/L with an ethanol subsidy of €150/t at different tax rates, and the other was an ESP of €0.60–0.70/L with the imposition of a €20/t gate fee. In the future, the addition of an integrated biofuel production operations unit, installed close to a pulp and paper mill, could utilize the different pulp side-streams and create further revenues to the mill owners.