Impact of a variety of forestry machine types on soil compaction is evaluated in this study according to the measurement of soil penetration resistance at 0 to 80 cm depth. It is concluded in the study that soils with poor bearing capacity (PBC), comparably small penetration resistance and organic layer thicker than 5 cm are less vulnerable to soil compaction. The use of small-size forwarder Vimek 610 allows to reduce soil compaction to an insignificant level in comparison to the control sites, and most or ruts disappear within a few days in PBC conditions. Whereas John Deere 810E, which belongs to the middle-size class of forwarders, significantly compacts soil through the whole measured depth in similar conditions. Rottne F10B and John Deere 810E forwarders represent the same weight category, and soil compaction due to the use of these machines on soils with moderate bearing capacity (MBC) is similar too; however, on soils with weak (WBC) and good (GBC) conditions results are different, mostly due to a different amount of extracted roundwood in both trials. Tracked forwarder was used only in GBC conditions and the results demonstrated significant compaction only down to 22 cm depth. The trials confirm that the depth of the intensity of impact depends on the weight of the machine and amount of material extracted; however, additional measurement data are necessary to characterize the impact quantitatively in different conditions.

Yasso07 soil carbon model was used to estimate soil carbon balance in dry forest site types (6 site types in total) in Latvia and the results were compared with data from Biosoil2012 soil surveys. Litter input, chemical quality and climatic data are required to run the model. Three different scenarios were used for climate data input – steady climate, climate change + 0.025 °C annually and climate change + 0.05 °C annually. Forest mineral soil is a carbon sink for the whole modelled period - the years of 1990 – 2030. Under steady climate, the average carbon removal is 0.6 t CO2 haE-1 yrE-1, under climate change (+ 0.025 °C) scenario 0.4 t CO2 haE-1 yrE-1, but under climate change (+ 0.05 °C) scenario 0.3 t CO2 haE-1 yrE-1. CO2 removal at the beginning of the period (1990) was 0.35 – 0.38 t CO2 haE-1 yrE-1. Carbon stock modelled with Yasso07 is lower than estimated in Biosoil2012 soil surveys. Differences between modelled and Biosoil2012 results vary from 2 t C haE-1 in the poorest and 41 t CO2 haE-1 in the third poorest site type. Carbon stock modelled with Yasso07 increases from the poorest to the most fertile site type while Biosoil2012 shows an increase from the poorest to the third poorest, and a decrease from the third poorest to the most fertile site type. Underestimation and different trends between Yasso07 and measured carbon stock may be explained by inappropriate equations and models used to estimate non-woody biomass. It is necessary to improve accuracy of input data for non-woody biomass by elaborating national equations and models in order to include Yasso07 in the national GHG inventory.

Wet soils play an important role in hydrological, biological and chemical processes, and knowledge on their spatial distribution is essential in forestry, agriculture and similar fields. Digital elevation models (DEM) and various hydrological indexes are used to perform water runoff and accumulation processes. The prerequisite for the calculation of the hydrological indexes is the most accurate representation of the Earth’s surface in the DEM, which must be corrected as necessary to remove surface artefacts that create a dam effect. In addition, different resolutions for DEM give different results, so it is necessary to evaluate what resolution data is needed for a particular study. The aim of this study is to evaluate the feasibility of using existing ditch vector data for DEM correction and the resulting implications for soil moisture prediction. Applied methodology uses a network of available ditch vectors and creates gaps in the overlapping parts of the DEM. The data were processed using open source GIS software QGIS, GRASS GIS and Whitebox GAT. Ditch vector data were obtained from JSC Latvian State Forests and the Latvian Geospatial Information Agency. The results show that by applying the bottomless ditch approach in forest lands on moraine deposits, depending on the accuracy of the ditch vector data, the values of the prediction of the soil wetness both increase and decrease. On the other hand, in forest lands on graciolimnic sediments it is visible that predicted soil wetness values increase in the close proximity of ditches. For forest lands on glaciofluvial and eolitic sediments there were no visible changes because of lack of ditches.

The analysis of regeneration processes on post-agrogenic lands allows establishing patterns and features of succession processes in phytocenosis, to identify the most appropriate measures to promote natural regeneration and to establish the possibility and feasibility of the production of forestry crops on lands left out of agricultural use. A study of forest regeneration processes in areas of fallow land for agricultural purposes adjacent to the floodplain of the Oredezh River in Gatchina district of Leningrad region. On the prepared study plots (0.25 ha) in different elements of the slope relief, the natural regeneration of pine and spruce and living ground cover was also taken into account. The soils on the objects of the study are agricultural soils of different thickness, from 30 to 45 cm. In two areas the soil is turfy, well-cultivated, concealed podzolic, ferrous illuvial soil on sands. On plots No. 3–5, the soil is turfy, well-cultivated, concealed podzolic, ferrous illuvial, clayey, on a red loam. The purpose of the study was to identify the nature of forest regeneration processes in areas of fallow land for agricultural purposes. It has been established that the composition of the emerging undergrowth depends on a number of factors: the type of soil, the taxation characteristics of the adjacent forest, the forest vegetation subzone, and the living ground cover. In these soil conditions on the deposits, young mixed undergrowth with a predominance of spruce and pine after a meadow stage of ruderal vegetation is formed.

Conifer tree stumps are a prospective source of bioenergy, but there are considerable uncertainties and risks associated with this forestry practice, and environmental consequences of stump harvesting are little studied in the Baltic countries. One of the major concerns is related to the risk of nutrient leaching that may cause pollution of watercourses and decline of tree growth in the next forest generation. The main aim of the present study was to estimate the effect of stump harvesting on general soil and soil solution parameters in three clear-cut areas located in Hylocomiosa site type (dominant tree species prior to clearfelling – Picea abies L. (Karst.)) over a period of 6 years after the stump removal. Two types of treatments were compared: whole-tree harvesting with only above-ground biomass removed (WTH) and whole-tree harvesting combined with the stump removal (WTH+SB). We found no acidification effect of soil and soil solution. Soil C and N stocks six years after harvesting were similar in the plots with and without stump removal, and demonstrated similar pattern of change in both studied treatments (WTH and WTH+SB). Nutrient content and patterns of change varied with the site and year, suggesting that the effects are rather site- than treatment-specific.

Enhanced forest growth may respond to demand of woody resources and contribute to the climate change mitigation. Forest soil treatment with fertilizers, as well as drainage and thinning enhance forest growth. The analysis of needles is an established method in forest science to identify the nutrient status in the forest stand and need for forest soil enrichment with fertilizers. The aim of this research is to estimate the efficiency of forest soil enrichment with wood ash and ammonium nitrate in order to eliminate nutrient deficiency in forest stands. Forest soil was enriched with wood ash fertilizer or ammonium nitrate in 2016–2017. The current year needles were collected from fertilized and control plots, from three trees in each plot. The samples were collected in the period 2018–2019. Total nitrogen (g kgE−1), calcium (g kgE−1), magnesium (g kgE−1), and potassium (g kgE−1) were analysed in the collected samples. The chemical properties of collected needles were compared at the individual object level to estimate the impact of fertilizer on forest stand. A statistically significant increase in the concentrations of potassium and phosphorus was detected in some plots treated with wood ash and ammonium nitrate. In addition, a correlation analysis conducted between the variables of chemical properties of needles and soil showed few significant correlations between nutrient content in needles and in soil samples.

The purpose of the study was to compare forest and postagrogenic soils by parameters such as carbon content in organic matter and total nitrogen to predict the fertility state of lands that are at the stage of restoration of woody vegetation. Areas with similar soil formation conditions were selected on the postagrogenic and forested lands having mature forest stands related with such types of forest: Myrtillosum forest, Oxalidosum and Herbosa-Composita forest, and also areas under the soil complexes of postagrogenic fallow lands. A number of physico-chemical indicators for the soil were assessed according to the methods generally accepted in soil science: the particle size distribution, the bulk density and the thickness of the pedogenic horizons were determined. An analysis of the carbon stocks in organic matter (Corg) and nitrogen (Ntotal) in the genetic horizons of the soils of myrtillosum, Oxalidosum and Herbosa-Composita forest types shows an increase in the content of organic matter and total nitrogen from Myrtillosum to Herbosa-Composita forest type. A comparative analysis of the physical and agrochemical state of postagrogenic and forest soils showed that, despite the previous anthropogenic impact, the agroland horizon retains a high content of organic matter and total nitrogen. The properties of postagrogenic soils in the studied areas are not deteriorated, and the transformation towards the natural forest soils of the region is not observed, despite the long period of fallowing.

The aim of the study is to evaluate carbon stock in litter and organic forest soils in Latvia as well as to characterize accumulation of carbon in litter in afforested lands. The study is providing empirically valid information about soil and litter carbon changes for the National greenhouse gas (GHG) inventory by using data from National forest inventory (NFI), forest soil monitoring demonstration project BioSoil and other studies. The study proves significance of organic forest soil carbon pool in Latvia and demonstrates necessity to extend NFI incorporated forest soil monitoring program to improve data on soil density in wet organic soils, as well as to integrate data characterizing water regime in forests. The acquired data also proves that the conservative approach of calculation of carbon stock changes in litter in afforested lands applied in the Latvia’s National GHG inventory avoids overestimation of CO2 removals. The data on litter carbon stock collected in this study is sufficient to estimate total carbon stock for stands dominated by most common tree species and long term impact of changes of species composition. Measurements of organic soil and litter thickness should be continued by NFI and integrated with more detailed soil monitoring to increase accuracy of carbon stock estimates and gather data necessary for verification of modelling data, particularly in afforested lands and due to change of dominant species.

A demand for wood resources is increasing. In addition to drainage and appropriate regeneration and thinning, the forest soil fertilization may increase the future harvest rates. Therefore, the improved growth of forest stands raises in priority among the research topics related to forestry. The objective of the study is to evaluate the impact of nitrogen fertilizer on soil water and throughfall water chemical composition to elaborate recommendations for the forest fertilization. The trials were conducted in a birch stand and in three coniferous stands. Nitrogen containing mineral fertilizer (ammonium nitrate) was distributed in the study sites, while the control plots were left without any treatment. The water samples were collected a season before and a season after the soil treatment. The pH level, total nitrogen, potassium and phosphate were determined in throughfall and soil water samples. The chemical properties of throughfall water differed depending on the forest stand type. The concentration of nitrogen was higher in throughfall water samples collected from the birch stand. The mean concentration of total nitrogen was 1.6 ± 0.3 mg LE−1 in the throughfall water samples from the birch stand compared to 1.03 ± 0.11 mg LE−1 in the throughfall water samples from the coniferous stands. Although the forest soil was enriched with the nitrogen fertilizer, there was a significant increase in concentrations of potassium and phosphate in soil water samples from certain stands. It can be explained with changes in pH level that occurred after the forest soil treatment with ammonium nitrate. There was also a significant increase in total nitrogen concentrations in soil water samples at the depth of 30 cm from the treated plots of the coniferous stands – 15 ± 6 mg LE−1, compared to 1.5 ± 0.03 mg LE−1 in the samples from the control plots. However, the concentrations decreased within two months and remained at a steady rate – slightly above the control level.

Forest mineral soil is one of the terrestrial carbon pools, and changes in forest management practices can affect the carbon stock in forest soil. The purpose of the study is to estimate temporal fertilization impact on mineral soil organic carbon stock, depending on fertilizers applied, forest stand type, different dominant tree species of the stands. Coniferous and birch forest stands with mineral soil in the central and eastern part of Latvia were selected for the experiment. The fertilizers used were wood ash and nitrogen containing mineral fertilizer. No significant differences in organic carbon stock in O horizon were detected 2–5 years after fertilization. A tendency of smaller organic carbon stock in upper mineral soil layers (0–10 cm, 10–20 cm) was found in most part of objects. Significantly smaller organic carbon stock was found in upper mineral soil layers (0–10 cm and 10–20 cm) in birch stands with wet mineral soil treated with ammonium nitrate if compared to the control plots, possibly due to a different soil moisture regime of forest stands. The positive and significant correlations between soil organic carbon and nitrogen stocks were found in most part of the objects.