Both forestry theory and practice have proved that amelioration favours the growth of forest stands significantly. The growing stock increases even 10 times, if the amelioration system is well-functioning. Joint Stock Company Latvia State Forests that is managing half of forests in Latvia has started renovation of old amelioration systems aiming to improve the productivity of state owned forests in Latvia. In order to evaluate the impact of the renovation of the old amelioration systems, a tree ring width in 7 pine stands, 5 spruce stands and 3 birch stands was analysed. This study shows that the renovation itself has not affected the productivity of mature pine, spruce and birch significantly 3-4 years after the renovation. Authors have come to a conclusion that the reason for that could be too short observation period or particularities of a stand structure and age.

This research deals with tendencies of growth of Norway spruce Picea abies (L.) Karst. during last 50 years (1960 – 2010) in eastern part of Latvia emphasizing trendal specificity of active periods during the first (t1: 1960-1985) and the second (t2: 1986-2010) time interval. There have been 150 superior stand trees bored in six mixed pine-spruce Pinus sylvestris L. – Picea abies (L.) H.Karst. stands. An active period of factor’s impact is the time span when some meteorological factor (decade average, minimal or maximal temperature and sum of decade precipitation) influences an increase of annual ring width significantly. Comparing average temperatures from two weather stations included in this research the difference between interval t1 and t2 is approximately 1 °C. Active periods of temperature impact on growth of Norway spruce in eastern part of Latvia during last decades have changed not only their location but also an impact direction from positive to negative. Minimal and maximal decade temperatures are those mostly determinating the radial growth of Norway spruce in the eastern part of Latvia. Interval t2 is quite rich in active periods both from minimal and maximal decade temperature. Research results prove hypothesis about trendal shift of meteorological factors’ impact active periods due to climate change. An increase in decade precipitation level in winter caused annual ring growth positively both in the interval t1 as well as in t2.

The influence of coniferous stand composition on the density of pine (Pinus sylvestris) and spruce (Picea abies) wood is considered in this work. Processing of a large quantitative material of wood cores with the use of the ANOVA and rank analysis made it possible to reveal the influence on the macrostructure of wood of the quantitative representation of pine and spruce in the stand. In the pine part of the stand, the correlation of the wood density with the zones of early and late xylem is weak or medium. There is no wood density correlation with the width of the annual ring for stands with different shares of pine. In pine-prevailing stands with a share of pine 80% – 100%, there is a weak but reliably straight relationship between wood density and the size of late wood zone and an inverse relationship with early zone of xylem. For forest stands with a smaller part of pine participation, the relationship between these indicators is medium and reliable. For spruce, we observe a close relationship between the density of xylem and the parameters of its macrostructure in all its variants of participation in mixed coniferous plantations. In most of the studied mixed stands, the density of wood in spruce is not significantly differentiated and more homogeneous.

The introduction of non-native tree species has been used as a climate change mitigation tool. To ensure the anticipated benefits, the analysis of species radial growth reactions to meteorological factors should be carried out. Initially, tree species were introduced to non-native regions as food resources, yet the focus has now shifted towards favourable wood properties and growth rates. This study used tree ring width measurements of Japanese walnut Juglans ailantifolia and climate data to examine the relationships between these variables. A total of 30 trees were sampled from a stand located in the southern part of Latvia. Tree ring width (TRW) was measured, and residual chronology was derived. Pearson correlation analysis was used to detect the correlating meteorological factors, and a linear mixed-effects model was used to detect the key factors. The correlation analysis indicated generally low correlation coefficients between TRW and meteorological factors, primarily correlating with summer precipitation, both the current and preceding summer, highlighting carry-over effects. Furthermore, signature years underscored the negative effect of low temperatures and summer droughts on the radial growth of Japanese walnuts. However, the observed variation in TRW between years, not fully explained by meteorological factors, suggests a dynamic rather than stable relationship.

The phenomenon of global climate change holds utmost importance in its impact on forest ecosystems. To mitigate the effects of this phenomenon, several European countries have introduced non-native tree species into their forests. However, comprehensive ecological analysis is needed to assess the suitability of these non-native species. Pinus strobus is often considered a potential substitute for native species. Tree-ring analysis is a useful methodology for evaluating the relationship between tree growth and meteorological conditions, given the significant impact of these conditions on tree development. In this study, 25 core samples were collected from an experimental plantation of Pinus strobus located in the western part of Latvia for analysis. The plasticity of the tree-ring width of Pinus strobus was evaluated using a multiple additive regression model. The analysis revealed that the previous summer precipitation was a significant factor, indicating the drought sensitivity of the increment. Additionally, the temperature in the previous July and August was also found to be a significant meteorological parameter, suggesting some tradeoffs between growth and the formation of nutrient reserves. The estimated growth responses suggest that the radial increment of Pinus strobus growing outside its native range is highly weather-sensitive, implying uncertainty in its growth with anticipated climatic changes. These findings emphasize the need for further ecological analysis to determine the suitability of non-native tree species and their ability to withstand the climatic changes.