Frost hardiness (FH) is one of the limiting factors for the successful growth of woody plants in the boreal zone. To cultivate the plants in cold conditions, they need to be tested before they are launched to the farmers and forest owners. Appropriate preconditioning for the different progenies of the plus tree of forest seedlings within the same species, and different horticultural woody species and cultivars are not known well. To answer those questions, this study designed and implemented experiments for Scots pine (Pinus sylvestris L.) progenies, for three horticultural species, i.e., apple (Malus domestica Borkh.), blueberry (Vaccinium corymbosum L.), blackcurrant (Ribes nigrum L.), and for pear cultivars (Pyrus communis L.). The study is composed of three parts with the following aims: i) to determine whether the pollination site affects the FH of the Scots pine progenies, ii) to determine the proper late-autumn preconditioning before running the frost hardiness tests of different apple, blueberry, and blackcurrant cultivars, and iii) to determine the effects of a short warm spell in mid-winter on the FH of pear cultivars. One of the important aims of the thesis was to assess and compare the different FH testing methods with the help of the experiments executed here.
The first part of the study consisted of the progenies of Scots pine plus-tree seed orchards in Finland and Ukraine, in addition to the progenies from natural stands in Finland, with three seed lots from each site. FH was examined twice during cold acclimation in controlled conditions. The second part concerned the effects of different preconditioning temperatures (+3, −3, −7, and −10 °C) and their durations (one or three weeks) on the FH of two apple cultivars, three blueberry cultivars, and three blackcurrant cultivars. The third part concerned the effects of short term warm spells in mid-winter on the FH of three pear cultivars that were preconditioned in natural conditions, then dehardened in a growth chamber at +5 °C for either 3-4 days or 16 days, and then rehardened at −7 °C for 5-7 days.
It was found that the freezing test temperature had a strong effect on the physiology and growth of different organs of the plus-tree progenies of Scots pine, but no consistent differences were found in FH among the progenies. The proper preconditioning temperature for the development of the maximum frost hardiness of the aboveground parts in late autumn is three weeks at −3 °C for apple and blueberry, though a shorter time for blackcurrant would be enough. The frost hardiness of the pear cultivars responded to temperature changes in mid-winter, but less than expected, and the responses were similar in all cultivars. In addition, the FH estimates of the stem by electrical impedance spectroscopy (EIS) and relative electrolyte leakage (REL) were quite similar, but these methods overestimated FH when compared to the FH by visual damage scoring. DTA results had a small variation compared to other methods but the use of DTA is limited due to the low occurrence rate of the low temperature exotherm (LTE) in several species (e.g., blackcurrant).
Ozone (O3) and nitrogen oxides (NOx: nitrogen monoxide NO and nitrogen dioxide NO2) are reactive gases with an important role in atmospheric chemistry. Terpenes are a reactive subgroup of BVOCs (biogenic volatile organic compounds) emitted by plants. Needle or leaf surfaces are the first point of contact between the atmosphere and a plant. Boreal forests represent a significant portion of the global land area available for atmosphere-biosphere interactions.
The aim was to develop methods for observing the exchange of NOx in field conditions and to explore the roles of terpenes on needle surfaces and nitrate fertilization on the fate of O3 and NOx in plant-soil-atmosphere interfaces. The methods included whole-canopy measurements, shoot-scale chamber measurements, needle sampling and laboratory analyses, utilizing both continuous observations and experimental setups.
In the studied low- NOx environment, the shoot-level NOx fluxes were too small to be monitored accurately in field conditions with an automated dynamic chamber. In addition to interference, the signal to noise ratio was low, and a significant proportion of the observed fluxes were to/from chamber walls. No clear NOx fluxes from Scots pine foliage were detected, and there was no effect of nitrogen fertilization on the observed fluxes. It seems unlikely that a fertilization treatment could cause significant NOx emission from boreal pine forests. The fluxes reported in our earlier studies included compounds other than NOx.
Shoot terpene emissions and needle wax extracts were both dominated by monoterpenes. There was variation in the terpene spectra of both emissions and wax extracts. The proportion of sesquiterpenes was higher in the epicuticular waxes than emissions, and the observed sesquiterpene compounds were for the most part different in the emissions and wax extracts. The role of direct transport through the cuticle from sites of terpene synthesis may be more important than has been assumed.
The involvement of local people in the governance process, reliable and transparent engagement of disadvantaged people in decision-making and justice in benefit sharing have been the emerging strategies for the acceptance of REDD+ (Reducing Emissions from Deforestation and Forest Degradation, forest conservation, sustainable management of forests and enhancement of carbon stocks). However, closer scrutiny of the values of forest governance is needed in order to evaluate its effectiveness, contribute to its legitimacy and understand the interactions of governance attributes. At the same time, both at the international and national level, there is lack of clarity around the kinds of governance arrangements that can be implemented at the ground when striving for REDD+.
This PhD thesis assesses the practicability and priorities of community forestry governance to articulate climate change mitigation initiatives by forest users. The focus includes factors associated with benefit sharing process, patterns of engagement of disadvantaged groups in community forestry and the impact of REDD+ implementation on social inclusivity of community forest user groups in Nepal`s Terai region. The study is based on grounded theory of qualitative approaches that builds on case studies from three community forest user groups and REDD+ interventions. Through the lens of a theoretical framework of common resources governance, the study assesses the similarities and differences between policy goals and observations of forest governance values and their impacts. Second, the study explains the nature of factors affecting benefit sharing and their impacts under REDD+ and other benefit sharing process in community forestry. Third, the study explores how existing policies and practices engage Dalits in community forestry governance processes. Finally, the study investigates how social inclusivity under REDD+ enhances representation and deliberation of disadvantaged groups and requires responsiveness in community leaders within community forestry.
The study results are based on the focus group discussions, in-depth interviews and participant observation in three community forests of the Nepal´s Terai. Similarities and differences between the factors of forest governance are apparent within the specific conditions of each community. Qualitative differences in the implementation of governance initiatives have increased the level of dissatisfaction among the community forest users. Though poor users of community forest were highly dependent on forest resources, rich users benefit comparatively more due to their control over decision-making structures. The formal structures for engagement of disadvantaged groups in community forestry do not provide enough space for genuine participation. The benefits of REDD+ implementation have not trickled down as expected to ground level. However, the implementation of REDD+ has also positively supported governance in community forestry. Proportional representation of disadvantaged groups has been achieved but the criteria need revisiting to prioritize the inclusion of highly dependent users in community forestry.
Emissions of biogenic volatile organic compounds (BVOCs) cool down the global climate via their impacts on aerosol and cloud formation. Climate change will likely have a major impact on BVOC fluxes from the biosphere, including soils, due to temperature-driven plant biosynthesis of volatile organic compounds (VOCs), compound volatility and microbial activity. Soils are a poorly quantified source of VOCs, where the diversity of driving factors creates high spatial and temporal variability in soil VOC fluxes.
The aim of this study was to analyse the magnitude and variability of forest floor VOC fluxes, to determine the role of the boreal forest floor in the forest stand BVOC exchange and to estimate plant ecophysiological and microbiological processes, which drive forest floor VOC exchange. Forest floor VOC exchange was determined using a steady-state flow-through chamber technique coupled with mass spectrometry in the boreal and hemiboreal climates.
We revealed that the boreal forest floor contributes significantly to forest stand fluxes, but its importance varies between seasons. The forest floor accounted only a few per cent of the total forest stand fluxes of monoterpenes in summer, while in spring and autumn it could be up to 90%. The forest floor VOC exchange was stable between years, while fluxes had clear seasonal dynamic. Monoterpenes and oxygenated VOCs originated from fresh litter, microbial activity, and ground vegetation VOC biosynthesis. Air inside soil layers was found to contain diverse compounds. Forest floor VOC fluxes varied strongly depending on climate and tree species.
Atmospheric chemistry may be strongly affected by soils during periods when plant-related BVOC biosynthesis and fluxes are low. In the future, we need continuous and simultaneous VOC exchange measurements from forest floors and forest stands in various ecosystems and climate zones. The global budget for soil VOC emissions should also be defined based on existing studies.
Scenic beauty of forest stands and impact of management
The aim of this study was to find out what kind of forest is considered beautiful, and how forest management affects the scenic beauty. Differences between interest groups and the impact of season on scenic landscape were also examined. The research was a psycho-physical preference study, where the scenic quality of the landscape at the tree stand level was explained by descriptive variables of the forest, treatment and season. The study examined the landscape preferences of ordinary people rather than experts.
Photographs taken from the forest were used to evaluate scenic value in all sub-studies. The photographs represented typical tree species compositions, forest treatments and stages of stand development in Finnish commercial forests. The objects of the study were commercial forests, urban forests, and tourist areas. Local Finns and foreign tourists who arrived in Lapland evaluated the photographs.
The survey found that most people value large stems and relatively open forests. Reforestation always decreases the scenic value of the landscape. However, deterioration of scenic value after reforestation was short-lived if it is related to the entire rotation length. Natural regeneration is scenically clearly better than planting or seeding. The scenic value of the forest can also be increased by forest treatments, especially in dense untreated stands. Excessive stand density is particularly offending for Finnish. In other respects, the forest landscape preferences of Finns and foreign tourists seem to be very similar.
The mental images on the landscape effects of forest treatments were essentially very similar with the perceptions based on photographs - all the treatments, which evaluators thought to increase the beauty of the forests, increased it also on the basis of the image evaluation also in practice.
Predicting landscape value is not easy, because there are clear differences between different groups of people and, in particular, individuals in scenic valuations. For example, forest owners and forestry professionals feel the landscape effects of forest treatments more positive than other groups do. The study supports the view that the attitude towards forest management actions reflected in the perception of the landscape effects of treatments.
The study showed how unique and time bound the experience of the landscape is. The same stand of trees may be experienced in a very different way in summer and winter outfit. On average, commercial forests appear to be suitable for recreation and tourism clearly better in winter than in summer. The difference is particularly evident in reforestation areas.
The main aim of this study was to investigate the dynamics and biophysical controls of carbon, water and energy exchange over a semiarid shrub ecosystem in the Mu Us desert, northern China, using continuous eddy-covariance (EC) measurements. Specific objectives were as follows: (1) To examine intra-annual variations in net ecosystem CO2 exchange (NEE) and its biophysical controls (Paper I); (2) To quantify the diurnal and seasonal variations in surface energy-balance components, and to examine the partitioning of net radiation (Rn) among different energy components at diurnal and seasonal timescales (Paper II); and (3) To examine how ecosystem production and water use efficiency (WUE) vary inter-annually with contrasting precipitation (PPT) and soil moisture patterns (Paper III).
The results showed that, soil water content (i.e. at 30 cm depth, SWC_30), or water deficit, imposed a major control on the seasonal dynamics of carbon assimilation and energy partitioning. Water deficit (i.e. SWC_30 < 0.10 m3 m-3) was a major constraint over daytime NEE, and also interacted with other stresses, e.g. heat stress and photoinhibition (Paper I). Low soil moisture reduced the temperature sensitivity (Q10) of total ecosystem respiration (TER). Rain events triggered immediate pulses of carbon release from the ecosystem, followed by peaks of CO2 uptake 1–2 days later. Leaf area index (LAI) accounted for 45 and 65% of the seasonal variation in NEE and gross ecosystem production (GEP), respectively. On the other hand, sensible heat flux (H) exceeded latent heat flux (λE) during most time of the year (Paper II). The evaporative fraction (EF, i.e. λE/Rn), Priestley-Taylor coefficient (α), surface conductance (gs) and decoupling coefficient (Ω) all correlated positively with SWC_30 and LAI. The direct enhancement of λE by high vapor pressure deficit (VPD) was buffered by a concurrent suppression of gs, which controlled EF and α by mediating the effects of LAI, SWC_30 and VPD.
At the annual scale, net ecosystem production (NEP, here defined as −NEE) indicated a rapid shift from an annual sink of carbon in 2012 (NEP = 77 ± 10 g C m-2 yr-1) to a source of carbon in 2014 (NEP = -22 ± 5 g C m-2 yr-1), with the year 2013 being close to carbon neutral (NEP = -4 ± 10 g C m-2 yr-1) (Paper III). GEP, TER and evapotranspiration (ET) also declined over the three years. Suppressed annual carbon and water fluxes were observed in years with low spring soil moisture. GEP declined more than TER and ET, leading to reduced carbon sequestration and WUE (i.e. GEP/ET). Neither annual nor growing-season PPT amount could explain the year-to-year variation in carbon fluxes. ET was a better proxy for water available to ecosystem carbon exchange on an annual basis. Autumn soil moisture levels were carried over winter to spring, and affected the rates of leafout, plant growth and carbon uptake in the early- to mid-growing season.
The aims of the study were to identify factors related to temporal and spatial variation in forest soil CO2 efflux(Fs), compare measurement chambers, and to test effects of a climate change experiment. The study was based on four-year measurements in upland Scots pine forests.
Momentary plot averages of Fs ranged from 0.04 to 1.12 gCO2m−2 h−1 and annual estimates for the forested area from1750 to 2050 gCO2 m−2. Soil temperature was a dominant predictor of the temporal variation in Fs (R2=76–82%). A temperature and degree days model predicted Fs of independent data within 15% on the average but underestimated it during the peak efflux period (July–August), possibly because of seasonal pattern in growth of roots and mycorrhiza. A comparison sub-study indicated that the reliability of the measurement chambers was not related to the principle i.e. non-steady-state through-flow, non-steady-state non-through-flow or steady-state through-flow.
Spatial variability of Fs within 400 m2 plots in four stands was large; coefficients of variation (CV) ranged from 0.10 to 0.80, with growing season averages of 0.22–0.36. A positive spatial autocorrelation was found at short distances (3–8 m). In data from several stands, thickness of the humus layer explained 28% of the variation in Fs, and with the distance to the closest trees it explained 40%. Fs also correlated with root mass of the humus layer. Between-plot differences in Fs were small.
In the climate change experiment, CO2 enrichment and air warming consistently, but not always significantly,increased Fs in whole-tree chambers. Their combined effect was additive, with no interaction; i.e. +23–37% (elevated CO2), +27–43% (elevated temperature), and +35–59% (combined treatment), depending on year. Air warming was a significant factor in the 4-year data according to ANOVA. Temperature sensitivity of Fs under the warming, however, decreased in the second year.
Heterobasidion annosum s.l. is a serious forest pathogen that causes significant economic losses, especially in the Northern Hemisphere. In Finland, the H. annosum s.s. and H. parviporum within the Heterobasidion complex affect the growth and wood properties of Norway spruce (Picea abies (L.) Karst.) and its suitability for different industrial purposes. The main aim of this PhD thesis was to study the wood degradation (WD) caused by H. annosum s.l. and enzymatic hydrolysis under laboratory conditions in wood specimens representing different genotypes and crown types of Norway spruce, and at positions along the stem. Furthermore, the relationship between WD and different traits such as tree growth, physical properties and wood chemical composition, as well as the production of reducing sugars (RS), were also studied.
The WD differed between normal-crowned Norway spruce clones, but not between normal- and narrow-crowned trees. H. annosum s.s. caused a higher WD than H. parviporum. The WD was also affected by the position within the wood discs, along the stem and by the age of the sample trees. In older trees, samples taken near the pith were more degraded than those taken near the bark and vice versa. In younger trees, wood density correlated negatively with WD. Positive correlations were also observed between RS and WD, suggesting that genotypes susceptible to WD may represent desired raw material for some other industries in which the hydrolysis of the main wood components is essential (i.e., biorefining). To conclude, this thesis showed that the genotypic variation observed in breeding material may represent an advantage for forest tree breeding to control and avoid Heterobasidion attacks, especially when studied along with other important traits and considering silvicultural practices such as the thinning regime and rotation length that may affect WD risk by H. annosum.