Ecological restrictions in forest biomass extraction for a sustainable renewable energy production

Highlights

• Nutrients' mean content is differentiated among the aboveground biomass' parts.

• Foliage is the main carrier of the macronutrients in trees' aboveground biomass.

• Foliage extraction should be prevented as leaves are vital ecosystem's residues.

• Stem bark and foliage are main carriers of micronutrients in aboveground biomass.

• Stem should be extracted without bark, as stem bark is vital ecosystem's residue.

Abstract

Renewable Energy Sources investments are scaling up across the Mediterranean region. The small scale utilization of the forest biomass for bioenergy purposes could boost the socio-economic benefits in a decentralized level, tackle the energy poverty and reduce the forest fire risk. This research contributes to a more sustainable use of the forest biomass for bioenergy purposes. From plant tissues analysis was proven that both macronutrients and micronutrients are being allocated differently between the aboveground biomass parts. This knowledge of content differentiation and distribution of nutrients in aboveground biomass contributed to the creation of hierarchy content of significance and protection of those parts. The foliage is the main carrier of the macronutrients. The bark of the stem and the foliage are the main carriers of the micronutrients. Thus, foliage extraction should be strictly prevented. In addition, the stem should be extracted without the bark. The leaves and the stem bark are vital ecosystem's residues. Further analyses reveal remarkable knowledge for the integration of suitable silvicultural treatments for ecological managing of coppice forests, for the sustainability criteria of forest energy harvesting and the ecosystems' nutrient balance. Accordingly, practical implications are presented. The ecological restrictions of the present research can shape an ecological and modern legislation framework as regards the forest biomass extraction for energy purposes in Greece and enhance in parallel the forest management policy in the Mediterranean region. Finally, future challenges are presented.

Introduction

Energy from biomass in a sustainable frame leverages many benefits. Further autonomous generation of energy enhances social and environmental assets, such as employment, lessens the risk of forest fires and decreases hazardous by-products in energy generation [1]. Generally, biomass is utilized as fuel within the same area that has been created [2]. Consequently, biomass constitutes an additional value in rural areas as it involves workforce, especially in a localized level, further technical equipment and a variety of scientific fields. In addition, energy from such sources like wood produces further localized labour in the economy nationwide rather than other energy sources [3].

There's a general aspiration for an adjustable and trustworthy energy balance, environmental benefits and new trade schemes for particular biomass types, a further autonomy away from fossil fuels [2]. The fossil fuel independence is achievable to be escalated via major upgrades in thermal and energy conversion technology that also could extend the power production in a variety of plant types, which are based on biomass resources [2].

Utilization of the remaining forest biomass from particular silvicultural operations is expanding due to renewable nature of these sources, which also provide advantages for the environment and the community [4]. Energy branch obtains a significant role in financial growth and societal prosperity of Greek region [5]. This study has been carried out in Grevena, in a mountainous regional unit of Western Macedonia region, which includes one of the largest greek forest areas and simultaneously an extensive amount of forest biomass in the whole country.

Nutrition steadiness, reuse of ashes and generally suggestions for energy production using biomass from forest are core subjects that concern specific projects for a viable management of European forests [6]. Managers integrate practical knowledge, assimilate enlightenments of science investigation and meet social anticipation. An incessant procedure of progress is called Adaptive Forest Management [7]. So, environmental and bioenergy strategies could be acccomplished by integrating silvicultural operations and biomass utilization as elements of a generic forest management plan [8]. Also, a sustainable and ecological bioenergy framework is highly depended on spatial criteria too [9].

At the present time, forest management for multiple purposes is gaining additional notice [10]. Preservation of natural environment, the aesthetical pleasure, leisure activities and generally a tendency apart from traditional production of wood is formulating in some countries [11]. Such a balanced multi-perspective approach could be derived also from a sustainable bioenergy framework.

In order to assess management inferences, the allocation of nutrients and biomass of the species is essential and also requisite to ameliorate the comprehension of several ecological attributes [12]. The effects on nutrients and biodiversity of biomass harvest in forest ecosystems preoccupy continuous conversations [13]. As regards residues' harvest from forest ecosystems, the consequences of nutrient abstraction on stand's productivity are of principal consideration [6].

The forest ecosystem has the system of energy flow and the system of nutrient substances flow, which are connected. Consequently, when the biomass is extracted, then specific amounts of nutrients are removed too, which are partially compensated by the nutrients from the rain water, which reach the ground. Also partially these are compensated by nutrients from the biological and physiochemical processes in the soil, but mainly from the soil stocks. The conservation of the ecological balance and the soil's productivity depends on the composition and the amount of biomass that is extracted from the ecosystem [14]. For a sustainable forest management two principles are essential, the principle of the conservation of the ecosystem's ecological balance and the principle of the preservation of the soil productivity [14]. The nutrient accumulation in the biomass of the plant is the outcome of some processes which are influenced by the soil productivity, by plant genomes and by the environmental situations [15].

The ecosystem contains rules and restrictions, in order a sustainable biomass production and also a viable biomass utilization as a renewable energy source to be achieved. The examination of the differentiation of the nutrients' content and distribution among the aboveground biomass compartments aims at the development of a specific framework, which includes a further comprehension and a hierarchy of significance and protection of these compartments. This comprehensive framework strengthens the ecosystem's protection and moves forward the sustainable utilization of forest biomass.

This study focuses on the restrictions of the system in light of nutrient content and distribution in aboveground biomass resulting in biomass’ sustainable utilization as a renewable energy source. Such a sustainable bioenergy framework could integrate in a level the energy production from the biomass and the conservation of the nutrient balance in the forest ecosystem.

The detailed distribution of the macronutrients and micronutrients’ mean content and their differentiations among the parts of the aboveground biomass are novel results of the present study, since there is a scarcity of similar studies in Greece as regards the sustainable forest biomass harvesting for energy purposes. Greece is a Mediterranean country with primeval forests and agroforestry landscapes and thus the ecological restrictions in biomass extraction should be extensively enhanced by similar studies. The ecological management of the accumulated forest biomass could reduce the fuel of the lethal forest fires, which are increasing in Greece during the last decade, and produce at the same time clean energy in order to mitigate the climate change impacts on the Mediterranean region.

The results of this research are very important, as the research is focused on an oak forest in Greece. According to literature [16], 44% of the forests of Greece are oak forests. Moreover, the oak forests of a study [17] which took place in north-west Spain, contained larger amounts of nutrients per kg of biomass compared to other forest species. The aim of the current research is to investigate and highlight the ecological restrictions in forest biomass extraction for a sustainable renewable energy production in the Mediterranean region.