Biomass potential of forest residues in forests of Ukrainian Carpathians as a component of regional green economy

The biomass of forest wood residues (waste) in the Ukrainian Carpathians is now an important resource for ensuring energy security under martial law and the formation of strategic directions for energy independence from imported fossil energy resources and the development of a green economy. As a result of the study, the indicators of the total potential of wood biomass of forest wood residues in the forests of the Ukrainian Carpathians were established both in volumetric units and primary energy units. These indicators are differentiated by territorial administrative units of the region and predominant forest stands. The information basis for the assessment of these indicators was the research data on biometric assessment of trees collected in temporary trial plots, as well as mathematical dependencies of conversion factors of biomass components. The study found that the environmentally safe annual potential of the studied resource is about 800 thousand m3, or 7.7 PJ, which can be additionally involved in the process of generating heat or other types of energy. The results of the study of forest residues biomass potential are an informational component for the formation of a regional program for the development of forest bioenergy in the Carpathian region of Ukraine.


Introduction
Use of wood biomass from forest waste is currently not only one of the areas of renewable energy development and a component of green economy mechanisms, but also an important social area for ensuring energy security of Ukraine's population under martial law.An intensive development of the national renewable energy sector is linked, among other things, to the destruction of a significant number of energy infrastructure facilities during missile strikes on the territory of Ukraine.It also stimulates implementation of low-carbon production approaches, as envisaged by the Low-Carbon Development Strategy of Ukraine, and facilitates positive environmental impact in urbanized conditions.
An imbalance of the current paradigm of mankind's energy supply, based on the dominance of fossil fuel energy, is also noted in the Energy Report [1] by World Wildlife Fund (WWF) in cooperation with ECOFYS energy consulting agency.Due to the progressive global decline in reserves of non-renewable natural energy resources (gas, oil, coal) and the urgent need to reduce 1254 (2023) 012096 IOP Publishing doi:10.1088/1755-1315/1254/1/012096 2 harmful emissions, the challenge of using alternative fuels has become particularly relevant [2].Wood biomass from forest waste in forests of Ukrainian Carpathians, one of the most forested regions of the country, serves as an important renewable energy resource for the region's green economy and is an integral part of the national energy sector in the context of energy dependence on fossil energy resources.
The forests in Ukrainian Carpathians, accounting for over a third of Ukraine's wood biomass reserves, remain an important environmental and social factor in development of local communities in mountainous areas.This necessitates the application of environmentally sound approaches to use of forest resources, ensuring a balance between economic, social and environmental components of the regional mountain forest management system.
While focusing on resource potential of forest wood biomass, researchers often do not consider the environmental component of forest stands' functioning, omit the important role of forest residues in logged areas in forming stocks of mineral nutrients as a result of biodegradation [3,4].
Uncontrolled use of wood biomass for energy purposes may have negative consequences for forest plant communities.For example, according to the published research [5], an increase in volume of wood biomass harvesting in Swedish forests may have negative consequences for the environment, forest soil fertility, and conservation of forest biodiversity.Excessive use of logging residues may also have a negative impact on mammal populations [6] and the ability of forest plant communities to provide ecosystem services [7].
The use of wood biomass is characterized by different ways of converting it into heat, electricity, and other types of energy.At the same time, researchers from Latvia [8] prove the inefficiency of using wood biomass for electricity production and conclude that the transition to renewable energy without radical changes in the existing economic system in the country will further exacerbate the environmental problems of bioenergy.When using forest residues for biofuel production, it is also necessary to consider their qualimetric features.A high percentage of bark in forest residues causes the formation of a significant amount of ash in the course of their combustion, which requires an increase in cost of fuel boilers maintenance [9].
The prospects for use of logging residues for energy production were also noted by Spanish and Italian researchers [10], who concluded that use of forest residues from natural forests is more environmentally friendly than wood biomass obtained from energy plantations.Energy from wood biomass can serve as an indicator of energy sustainability in the face of current challenges (extreme weather events, climate change, environmental pollution, loss of biodiversity) [11].
In the process of assessing potential opportunities for involving wood biomass in the energy sector, the long-term planning process is important, given the environmental acceptability, economic feasibility and reliability of resource formation [12].This approach allows to involve the maximum number of stakeholders for the effective implementation of renewable energy technologies.Given that use of wood biomass as an energy resource ensures the development of low-carbon production, its sustainable use serves as a tool for mitigating global climate change.Thus, according to research by scientists from Thailand [13], if wood biomass is used for bioenergy production in Southeast Asia instead of burning coal, diesel or natural gas, the total emission reduction could be 229.9,215.4 or 207.9 Tg CO 2 per annuum.
Accumulation of wood biomass in the form of dead wood in forests with a significant anthropogenic load can contribute to an increase in fire hazard due to build-up of forest combustible materials stocks [14,15].Therefore, a portion of dead wood can be used as an energy resource without compromising biodiversity conservation.
Thus, based on the analysis of the literature, it can be concluded that forest biomass, including forest residues, remains on the agenda of global scientific community as a strategic renewable energy resource.At the same time, its use should be carried out in compliance with the conceptual framework of sustainable development.
The purpose of this research is to assess the potential of biomass of forest residues in forests of Ukrainian Carpathians as an important part of renewable energy resource and a component of regional green economy development.

Materials and methods
The research is focused on forest stands in Ukrainian Carpathians, which according to the information from the stand level database run by Industrial Association "Ukrderzhlisproekt" (Ukrainian Industrial Association for Forest Management Planning), cover an area of 2012.3 thousand hectares and feature growing stock of 577.5 million m 3 within four administrative regions (table 1).Spruce, beech, and fir stands predominate in the research region, accounting for about 70 % of forested area.Almost a half of these stands are mid-aged ones.To carry out the research of weight characteristics of biomass components, we used experimental data collected on temporary sample plots using a unified methodology [16].The total amount of experimental data used for the purposes of our research is 662 model trees, 513 experimental sections of tree trunks and 246 samples of crown branches (table 2).The research uses the statement that forest wood residues (waste) are primarily represented by wood raw materials harvested in the process of thinning (lighting, clearing and partially first commercial thinning) in the form of whole trees, as well as logging waste, logging residues (parts of trunks, branches, treetops, etc.), stumps and roots that are formed after final cuts, sanitary cuts and other forest tending and care measures.
To establish the total biomass stocks of crown branches, which form the bulk of forest wood residues volume in the forests of Ukrainian Carpathians, we used mathematical dependencies of biomass expansion factors tested for the territory of the research region [17].To estimate the energy potential of wood biomass of forest residues, we used a dependence that reflects the sum of its structural components and has the following form: where P F W W a , j -total energy potential of forest wood waste in year a over a territory j, m 3 ; P F P t a, j -potential of forest products harvested at thinning in young stands (lighting, clearing) in year a over a territory j, m 3 ; P F W a , j -potential of forest waste (parts of trunks, branches, treetops, etc.) in year a over a territory j, m 3 ; P SRS a , j -potential of stem residues and stumps in year a over a territory j, m 3 .

Results and discussion
Using information on biometric characteristics of forest stands obtained within the framework of the current State Forest Account and the proposed modeling tools [18], it was found that the total biomass of crown branches in forests of Ukrainian Carpathians exceeds 50.0 million tons of dry matter (table 3).Nearly 45 % of the biomass is accumulated in stands of Zakarpattia region, where its density is 3.8 kg • (m 2 ) −1 .This region is dominated by European beech stands (more than 60 % of forested area), which form a much larger crown compared to coniferous tree species.In general, in forests of Ukrainian Carpathians, the share of branches biomass of European beech is 58.2 %.Every year, more than 2.5 million m 3 of wood is harvested in the research region.As a result, a significant amount of forest wood residues is formed.They can serve as a significant source of energy resource that must be used in compliance with an ecologically balanced approach to nutrients cycling in forest plant communities while ensuring low fire hazard.
To assess the potential of wood biomass in forest residues in units of primary energy (Joules), quantitative values of energy content per unit volume (table 4) were established based on density of biomass components [18].The energy value of biomass was determined based on data by Shvidenko et al [17].In terms of energy value, 1 m 3 of wood over bark of European beech branches is equivalent to 310 m 3 of natural gas.In the research region, beech biomass has the highest consumer demand as an energy resource for heat production during the heating season.
A 110-120 years aged beech stand features the proportion of crown branches of about 20-25 % of its total stem stock.For spruce and fir, this figure is about 10-15 %.Currently, more than 80 % of logging residues remain on site after logging, some of them can be used for heat production without harming the environment.
The research resulted in an assessment of environmentally safe potential of wood biomass from forest wood residues.This type of energy potential accounts for requirements related to The energy value of the studied biomass potential of forest residues in forests of Ukrainian Carpathians is almost 7.7 PJ (table 6), which is roughly equivalent to more than 240 million m 3 of natural gas. of a developed network of high-quality forest roads.Here, 10 to 20 % of forest areas covered with forest vegetation remain technically inaccessible.An important precondition for efficient production of solid biofuels is creation of a closed technological cycle of wood processing, starting with logging and ending with processing of waste into pellets or other types of biofuels.The production process should start at a forest plot and a forest road.It should include all logistics and other stages that would guarantee high economic efficiency, low production costs and, ultimately, high price competitiveness compared to traditional energy resources.The system of financial and economic incentives for development of forest bioenergy in the region also needs to be optimized.Due to the lack of financial incentives for implementation of bioenergy projects from the state and local governments in the region, most of them are implemented with the support of foreign funds and programs.

Conclusions
The research results present quantitative values of biomass potential of forest wood residues in forests of Ukrainian Carpathians, which will serve as an information basis for formation of a strategy for development of regional forest bioenergy and green economy.In general, the total biomass of crown branches, as the main component of forest wood residues, is more than 50.0 million tons of dry matter.Almost half of this volume is accumulated in the stands of Zakarpattia region.The energy value of the biomass resource varies from 9.083 GJ • (m 3 ) −1 for Silver fir stands to 9.852 GJ • ( m 3 ) −1 for European beech s tands.In terms of energy value, 1 m 3 of wood over bark of European beech branches is equivalent to approximately 310 m 3 of natural gas.Currently, more than 80 % of logging residues are left for biodegradation at logging sites.According to the results of our research, more than 800 thousand m 3 of forest wood residues can be additionally used as a renewable energy resource without harming the environment and functioning of forest plant communities in the region.In energy terms, this is almost 7.7 PJ, or approximately more than 240 million m 3 of natural gas.At the same time, to facilitate the efficient us e of th is re source, it is ne cessary to en sure co mpliance wi th th e ba sic principles of sustainable development of the mountainous region, balancing its economic, environmental and social aspects.State regulation, regulatory support, financial a nd e conomic i ncentives for development of forest bioenergy are necessary in the region.Also, development of wood biomass processing technologies as well as development of regulatory and information tools for assessing and monitoring energy potential of forest biomass are of crucial importance.Implementation of the above framework recommendations will facilitate implementation of positive systematic changes in the renewable energy sector, enable accounting for energy needs of the society and uphold energy security principles during martial law.

Table 1 .
Quantitative characteristics of forest plots in the research region.

Table 2 .
Quantitative characteristics of forest plots in the research region.

Table 3 .
Biomass of crown branches in forests of Ukrainian Carpathians.

Table 4 .
Energy value of tree biomass components (crown branches).nutrients,biodiversityconservation, and compliance with environmental requirements for use of forest wood waste.It also takes into account orographic features of mountain forests.In total, more than 800 thousand m 3 (table5) of forest residues can be additionally used as a renewable energy resource annually.

Table 5 .
Biomass potential of forest residues in forests of Ukrainian Carpathians.

Table 6 .
Energy potential of forest wood residues biomass in the forests of the region.At the same time, the main problem of utilizing the assessed energy potential is the logistics of this resource to the end user.At present, one of the problems hindering the introduction of new technologies for energy use of wood in the Carpathian region of Ukraine is the lack