This study was designed to estimate the variation in non-volatile carbon (C) content in different above- and belowground tree parts (stem, living branches, dead branches, stumps, coarse roots and small roots) and to develop country-specific weighted mean C content values for the major tree species in hemiboreal forests in Latvia: Norway spruce (Picea abies (L.) H. Karst.), Scots pine (Pinus sylvestris L.), birch spp. (Betula spp.) and European aspen (Populus tremula L.). In total, 372 sample trees from 124 forest stands were selected and destructively sampled. As the tree samples were pre-treated by oven-drying before elemental analysis, the results of this study represent the non-volatile C fraction. Our findings indicate a significant variation in C content among the tree parts and studied species with a range of 504.6 ± 3.4 g·kg−1 (European aspen, coarse roots) to 550.6 ± 2.4 g·kg−1 (Scots pine, dead branches). The weighted mean C content values for whole trees ranged from 509.0 ± 1.6 g·kg−1 for European aspen to 533.2 ± 1.6 g·kg−1 for Scots pine. Only in Norway spruce was the whole tree C content significantly influenced by tree age and size. Our analysis revealed that the use of the Intergovernmental Panel on Climate Change (IPCC) default C content values recommended for temperate and boreal ecological zones leads to a 5.1% underestimation of C stock in living tree biomass in Latvia’s forests. Thus, the country-specific weighted mean C content values for major tree species we provide may improve the accuracy of National Greenhouse Gas Inventory estimates.

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 L-1 in the throughfall water samples from the birch stand compared to 1.03 ± 0.11 mg L-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 L-1 , compared to 1.5 ± 0.03 mg L-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.

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 CO 2 ha-1 yr-1 , under climate change (+ 0.025 °C) scenario 0.4 t CO 2 ha-1 yr-1 , but under climate change (+ 0.05 °C) scenario 0.3 t CO 2 ha-1 yr-1. CO 2 removal at the beginning of the period (1990) was 0.35-0.38 t CO 2 ha-1 yr-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 ha-1 in the poorest and 41 t CO 2 ha-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.

According to earlier studies, Logbear F4000 forwarder is suitable for extreme and bad forwarding conditions in pre-commercial and commercial thinning, but it can be also used in salvage loggings and, when necessary, in final felling; however, larger machines are recommended for the conventional final felling. The aim of the study is to test performance of the tracked forwarder Logbear F4000 in thinning in forest stands with moderate or bad forwarding conditions (on wet and drained mineral and organic soils), including productivity, fuel consumption, load capacity and forwarding costs. Trials were conducted in 2016 and 2017 by forwarding logs in thinning, where harvesting was done by Vimek 404 T5 (bad conditions) and John Deere 1070 harvester and chainsaws (moderate conditions). No significant difference was found in forwarding productivity, when logging was done with a chainsaw or a harvester. In moderate forwarding conditions the average load was 3.4 m 3 and the average driving speed was 77.5 m•min-1 , but in bad forwarding conditions the average load was 3.6 m 3 and the average driving speed was 45.0 m•min-1. According to the study, the productivity is significantly influenced by both, increase of the forwarding distance and the load size. The average fuel consumption of Logbear F4000 is 4.93 ± 0.26 (standard deviation) l per hour (1.14 ± 0.14 (standard deviation) l m-3). Prime cost of roundwood forwarding in bad forwarding conditions is 6.8 EUR•m-3 , in moderate conditions 7.9 EUR•m-3 , accordingly, and is significantly influenced by increase of the forwarding distance and reduction of payload.

Scots pine (Pinus sylvestris L.) is one of the most widespread and economically most important tree species in Latvia. Scots pine forest health and element flow changes have been monitored in Latvia within the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with assessment of crown condition and damaging agents at 115 Level I monitoring sites (mostly oligothrophic and mesotrophic Vacciniosa, Myrtillosa and Hylocomiosa forests) and with sampling and analyses of environmental samples at three Level II monitoring sites representing typical Scots pine forests (Myrtillosa) in hemiboreal conditions in Latvia. This study summarizes the background information and presents the trends of forest health, carbon turnover and environment condition in Scots pine forest since 2009. In general, defoliation rate in Scots pine stands remains stable for the studied period, with some yearly fluctuations, possibly related to regional insect outbreaks, especially well demonstrated in two Level II plots. The share of damaged trees varied by year from 12.8% to 19% of the total number; the main cause of damage was direct action of man. Chemical element flows in Scots pine forests in Level II monitoring plots have been relatively stable as well except the decreasing trend in total N concentration in deposition and SO4-S concentration in soil solution and increasing trends in DOC concentration in soil solution that is in line with common trends in Europe. Carbon input with above-ground litter was relatively stable during the whole period; however, interannual variations were rather wide.