Latvia's forest reference level (FRL) should take in account the future impact of dynamic age-related forest characteristics in order to avoid unduly constraining the forest management intensity as a core element of sustainable forest management practice, with the aim of maintaining or strengthening long-term carbon sinks. The basic for calculations of GHG projections is AGM (Forest growth model) and EPIM (Emissions Projections and Inventory Model). The scope of the study is to verify applicability of the AGM model in elaboration of the forestry projections for elaboration of the FRL according to regulation (EU) 2018/841.

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.

Fertilization is a method to enhance tree growth and timber production. Ammonium nitrate and wood ash are commonly used fertilizers, which can be applied at the same time to increase levels of both nitrogen and other macro- and micronutrients. We studied how ammonium nitrate and wood ash fertilization affects photosynthetic activity and transpiration at leaf level in a deciduous tree plantation in former agricultural land with mineral soil, located in the central part of Latvia (Keipene parish). Additionally, we performed foliar and soil nutrient analyses. Our results support the notion that nitrogen fertilization may not result in increased photosynthetic activity. It is possible that the photosynthetic activity has increased at canopy scale along with increasing leaf area, not at leaf scale. Wood ash addition seems to have resulted in higher photosynthetic activity for hybrid alder, although it could not be explained with phosphorus availability. Although closely related to photosynthesis, in most cases transpiration was not positively affected by fertilization. Environmental factors, such as humidity, temperature and wind speed may have a greater effect on this process.

The present study aimed to detect any changes in concentrations of nutrients and evaluate the impact on the quality of two hemiboreal streams that collect a discharge from two fertilized Scots pine stands. In 2017, nitrogen-containing mineral fertilizer was spread in pine stands on mineral soil located near the first stream. In 2018, potassium containing wood ash was spread in pine stands on organic soil near the second stream. From 2017 to 2020, surveys of physico-chemical parameters, diatoms, macrophytes, and macroinvertebrates were performed to determine the possible effects of fertilization on the ecological quality of the streams. A control site upstream of the fertilized forest stand and a treatment site downstream of the fertilized forest stand was monitored at each stream. Water quality indices, chemical parameters of surface water, and indicator species analysis showed no short-term impact of forest soil improvement with wood ash and ammonium nitrate. We found no clear patterns before and after the fertilization events in both streams, although we did observe inter- and intra-annual differences in aquatic biota and stream ecological quality mainly caused by local environmental factors.

Enhanced forest growth may respond to the increasing demand for wood resources. Moreover, the forest is considered to be carbon storage, thus contributing to climate change mitigation. The forest soil fertilization, as well as forest drainage, thinning and regeneration may be an effective measure in increasing harvest rates. In the context of bio-economy, wood ash needs to be managed and can be utilized as an equivalent to potassium and phosphorus containing fertilizer. Ammonium nitrate can be used as fertilizer in forests on mineral soil since nitrogen is considered to be a tree growth limiting element in boreal forests. However, environmental aspects like leaching of the fertilizer should be taken into account. The aim of this research is to evaluate the impact of wood ash, ammonium nitrate and combined wood ash and nitrogen fertilizer impact on the chemical properties of soil water in dominated forest site types in Latvia. The trials were conducted in total in 16 forest stands. The fertilizers were spread in treatment plots, but the control plots were left untreated. The soil water samples were collected for two seasons. The pH, potassium, calcium, magnesium, phosphate and total nitrogen were determined in the soil water samples. Ammonium nitrate had an impact on the elevated concentration of total nitrogen in all experimental objects; although the significant differences between the control plot and treated plot were detected only in a part of experimental objects. The elevated concentrations of total nitrogen decreased after two months and remained above the control level. Interestingly, we observed a trend of both – increased and decreased concentrations of potassium, calcium, magnesium and phosphate. Nevertheless, only a part of the differences was statistically significant. The impact of wood ash on chemical properties of soil water was less pronounced in comparison to ammonium nitrate.