For establishment and growth of newly planted seedlings it is essential to overcome environmental stress at the planting site. Adding the amino acid arginine at planting is a novel treatment aiming at increased establishment success, so far tested in a limited number of applied studies. We examined the effects of adding arginine-phosphate (arGrow (R)), mechanical site preparation (MSP), and planting time on survival and growth of Norway spruce and Scots pine seedlings in two field experiments in boreal southeastern Norway. After three growing seasons, survival for spring planted seedlings of both species was significantly better following MSP, while addition of arginine-phosphate did not have any effect. Autumn planted pine seedlings with MSP and arginine had higher survival and also larger diameter than spring planted ones with MSP but without arginine. Spruce and pine seedlings with MSP were taller and had larger diameter than those without MSP. For spring planted seedlings of both species, dry weight of roots and shoots was positively affected by MSP, but not by arginine. To conclude, arginine-phosphate had neutral to modestly positive effects on survival and growth, while MSP had clear positive effects. The effect of planting time varied with species.

Wildfires are an ever-increasing issue due to the driving forces of climate change. Weather events that lead to higher wildfire potential are likely to increase and thus new fire management methods via more sustainable fire suppressant class A foams rather than retardants are being developed. However, despite their adherence to regulations, foam impact on targeted ecosystems, namely forests and forest trees is poorly studied. We aimed to investigate how three tree species (Pinus sylvestris, Alnus glutinosa and Picea abies) will react to a one-time class A foam application. Two separate trials were conducted. During the first the foam was applied to seeds and during the other - to 1-year-old seedlings. Tree growth and physiological status were evaluated. Stress criteria for cellular damage, non-antioxidant and antioxidant stress response and photosynthesis efficacy were measured. Results showed an obvious species effect, as all three reacted differently. The dose effect was also notable, with the higher application rate leading to a proportionally bigger response. Overall, pines were negatively impacted, spruce were positively affected, and alders didn't experience a notable change. This leads us to conclude that pending the limitation of this experiment the tested foam while phytotoxic in some cases, is unlikely to affect tree survival rates under field conditions and any physiological responses are likely transient in nature.

Accurate knowledge of site conditions and their effects on regeneration establishment is important for selecting the most appropriate tree species and regeneration methods for a given regeneration site. This study examined the response of the first-year field performance of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth.) seedlings in boreal forests to variables available in open forest and natural resources datasets. Survival, height increment and damage of planted tree seedlings and the success of direct seeding of pine were analysed on a total of 284 plots (1000 m(2)) in 18 regeneration experiments established in 2020-2022 in southern and central Finland. The height increment of silver birch was higher than that of conifers, while the lowest mortality rate was found for spruce. In the generalised linear mixed models, topographic wetness index, soil texture, site type and growing stock at clearcut explained the species-specific survival and height increment of planted seedlings and the success of pine seeding. Low-cost, open geospatial data effectively provide useful details on the site conditions suitable for diversifying tree species composition in boreal forests instead of monocultures.

The growth peculiarities of Scots pine ( Pinus sylvestris L.) have been studied by the example of an even-aged pine stand of high density. A long-term research has been conducted on a permanent sample plot. The data has been collected from the stand aged from 37 to 55 years. The characteristics of individual trees and the entire stand during the growth period in the absence of external influences (cutting, windfalls, pest damage, etc.) and after improvement cuttings have been analyzed. The influence of the amount of resource available to a tree on the formation of crowns, root systems and stem wood has been investigated. The size of the available resource has been the square of the dominance area. The root system of the pine trees of the studied stands is compact in size and, despite the high stand density, due to the high content of nutrients in the soil and the absence of moisture deficiency, it sufficiently ensures intensive tree growth corresponding to the conditions of the I quality class. It has been found that under these conditions, the average area of the root system is proportional to the average square of the dominance area. It has been shown that the stem diameter at a height of 1.3 m in the absence of external influences significantly depends on the square of the dominance area. The correlation coefficient of these indicators for the studied stand at the age of 37 is 0.89. The influence of cuttings on annual radial increment has been studied using dendrochronology methods. It has been revealed that in the year following the cutting, it has increased by 1.3-2.0 times, depending on the increase in the square of the dominance area. A method has been proposed for calculating the competition coefficient as a share of the resource required for the free growth of a tree, which is redistributed between its closest neighbours. Long-term observations have shown that with competition coefficients exceeding 0.6-0.7, the stem diameter increment rate decreases significantly, and the trees develop a sparse crown extending less than 40 % of the tree height. This, in turn, leads to growth retardation and a transition to a depressed state. This, in turn, leads to growth retardation and a transition to a depressed state.

In northern boreal forests the warming winter climate leads to more frequent snowmelt, rain-on-snow events and freeze-thaw cycles. This may be harmful or even lethal for tree seedlings that spend even a half of the year under snow. We conducted a snow cover manipulation experiment in a natural forest to find out how changing snow conditions affect young Scots pine (Pinus sylvestris L.) seedlings. The ice encasement (IE), absence of snow (NoSNOW) and snow compaction (COMP) treatments affected ground level temperature, ground frost and subnivean gas concentrations compared to the ambient snow cover (AMB) and led to the increased physical damage and mortality of seedlings. The expression responses of 28 genes related to circadian clock, aerobic and anaerobic energy metabolism, carbohydrate metabolism and stress protection revealed that seedlings were exposed to different stresses in a complex way depending on the thickness and quality of the snow cover. The IE treatment caused hypoxic stress and probably affected roots which resulted in reduced water uptake in the beginning of the growing season. Without protective snowpack in NoSNOW seedlings suffered from cold and drought stresses. The combination of hypoxic and cold stresses in COMP evoked unique transcriptional responses including oxidative stress. Snow cover manipulation induced changes in the expression of several circadian clock related genes suggested that photoreceptors and the circadian clock system play an essential role in the adaptation of Scots pine seedlings to stresses under different snow conditions. Our findings show that warming winter climate alters snow conditions and consequently causes Scots pine seedlings various abiotic stresses, whose effects extend from overwintering to the following growing season.