It is usual that when a new source of biomass is identified as a potential interesting resource, to pose questions like next: Is this biomass resource actually a feasible and interesting feedstock for the inhabitants in a region? Should it be taken into account as a realistic alternative energy resource?

Picture 1: Inventorying work for roadside vegetaion in Rotenburg (Wümme) 

Picture 1: Inventorying work for roadside vegetaion in Rotenburg (Wümme)

The assessment of the relevance and potential of a biomass resource for a specific territory is made up of two components. First, the amount of resource needs to be quantified. This parameter can be estimated according to its extent (area occupied by an ecosystem, like hectares of forest), or according to the planned maintenance work to be carried out yearly. Second, it must be ensured that the biomass resource is not only existing in relevant amounts, but also that its utilisation is feasible.

Special care should be taken into account when identifying new biomass resources. Being too optimistic can create too high and unrealistic expectations, which can lead the biomass to be taken into account as a key resource in the regional energy planning, conducting even to the promotion of entrepreneurship. If the potentials were wrongly obtained they may lead to a successive list of frustrated initiatives. As a result the sectors involved become more aware of the false expectations and reluctant to be involved in the future in other biomass initiatives. A social barrier for the future utilisation of biomass resources may be established, causing a stuck of the biomass utilisation in the region.

The aim of the present article is to provide some hints to contribute to more reliable biomass assessments and to call upon responsibility when implementing them. Below, ,the greenGain methodology for obtaining the biomass assessments in the seven model regions of the project is explained in a stepwise approach.

Step 1: Status quo 

Before performing any further assessment it is crucial to carry out a general identification of the LCMW biomass framework including information related to how widely it is extended in the local territory, or how many areas are object of treatment; who is the owner, who programs the works and who executes it; if the treatments are object of any regulation; how are the treatments usually executed, and how is the residual biomass currently handled; and determine if the LCMW biomass has been already object of any use in the area.

The status quo has been the starting point for the greenGain assessments and makes a very significant contribution to further work. From a total of 18 LCMW biomass types pre-identified in the pilot regions, six of them were already observed as un-relevant for the regions. Few of them were either re-grouped, or disaggregated (e.g.: firewall opening and firewall maintenance, which share part of the legal framework, but for which obtaining the biomass requires different operations). As well several new biomass types were identified as relevant, and so, added to the set of LCMW to be analysed by the pilot region.

Step 2: LCMW spatial dimensions 

The total potential of a bio-resource is a second cornerstone. For its assessment it is necessary to identify the targeted areas to be treated and the potential production of biomass per unit of treated area.

For this purpose greenGain partners have carried out multiple contacts with the authorities or companies in charge of the planning and performance of the conservation and maintenance work of every LCMW biomass type. The data obtained consists of areas which are object of treatment (in maps format, or inventories by municipality or county), historical records of treatments (allowing observation of trends and inter annual variations) and treatment planning (for one or several years). The analysis of historical records and future planning allows a better interpretation of the total potential areas, and therefore, to understand the actual dimension or relevance for the production of biomass.

Among the considerations of greenGain it has been stated that some treatments are being considered to be extinguished in future, as the territory does not require creation of new infrastructures (general case of auxiliary belts in the Spanish regions). Some other types, on the contrary, are being considered to require action, and so, plans for optimizing the treatments are being settled, like in the case of cleaning forests in moors to secure drainage in Friesland and Rotenburg (Wümme) (German model regions).

A good practice is to carry out specific inventories for those genuine targeted areas for which input data is scarce or just non-existent. For example in the Region of Rotenburg (Wümme), COALS (greenGain partner) already carried out an inventory on the woody vegetation along the roads in past years. They prepared a randomised sampling on 300 points in their targeted road networks, measuring the length of vegetation aligned in 200 linear meters of road, the type of vegetation density and the urgency of treatment (next intervention in the next 10 years). In the Spanish regions, it is expected to carry out the inventory of 8 km of river, detecting the areas where the river basin is invaded by wild reeds.

Step 3: Biomass production rate per treatment  

Picture 2: Inventorying work for roadside vegetaion in Rotenburg (Wümme) 

Picture 2: Inventorying work for roadside vegetaion in Rotenburg (Wümme)

How to obtain relevant data? Some best practices. 

Obtaining accurate rates of biomass production per treatment is usually challenging, especially when no biomass utilisation has been carried out before. In case of forestry related LCMW biomass the utilisation of forestry inventories and the expertise of service companies is a good alternative. Forestry inventories have usually a good estimation of the volumes of wood, and provide data regarding the forest vegetation strata. By identifying the forestry operations to be carried according to the forestry state, the amounts of biomass obtained can be estimated in each targeted area.

Which procedure should be used in case no inventories are available? This is the most common case for LCMW biomass. It is likely to know the targeted areas, but not the vegetation existing in these areas. Some hints regarding how to proceed are presented below:

  • Resources being already object of treatment for years: in such cases the companies executing the works may have measured indirectly the amounts obtained. For example, when biomass residues obtained from riverside, roadside or parks must be disposed, companies shall have an accounting of mass or volumes yearly disposed. This is a key data from where to start. The biomass estimation for parks, riversides and roadsides in Trasimeno (greenGain model region in Italy) has already proceeded according to this approach. The validation of the data obtained is currently under process.
  • Resources not being object of treatment: the best practice is to carry out samplings. This is the case proposed by greenGain in the Spanish pilot regions of Matarraña and Bajo Aragón, where it is planned to get some preliminary samples of reeds in order to determine the riverside cleaning biomass ratio. A first sampling has been already carried out by CIRCE in Zaragoza to prepare the sampling and weighing methodology.
Picture 3: Biomass sampling for wild reed in Zaragoza (Spain).

Picture 3: Biomass sampling for wild reed in Zaragoza (Spain).

Picture 4: Biomass sampling for wild reed in Zaragoza (Spain).

Picture 4: Biomass sampling for wild reed in Zaragoza (Spain).

Some very uncertain practices: 

Thumb rules and personal visions are other usual practices involving high uncertainty, which should be considered a “last resource” approach to carry out the biomass potential estimations. Exemplifications of practices to be avoided are shown below:

  • Visual estimations: it is an extended practice to ask the persons or companies executing the work about the amount of biomass produced. They may have never thought about it, and their estimations will be based on visual perceptions. An example could be the pruning carried out by farmers in vineyards. They may estimate the kg of branches per vineyard stock. Farmers might have never weighted the branches, and estimations range from 1 to 2 kg per vine, which implies from 2 to 4 tons per hectare if the plantation has a density of 2,000 vines per hectare. However based on this estimation, vineyards with 800 vines per hectare, would produce from 0.8 to 1.6 t/ha. And vineyards with 3,000 vines per hectare, from 3 to 6 t/ha. This is, however, not the case, and more and less dense vineyards do not necessarily produce more biomass per hectare. . Additionally, the uncertainty should be considered. The appraisal given by the farmer is uncertain, and he might have overestimated the production. In case the actual pruning ratio by vine stock had been  0.5 kg/vine instead of 1-2kg per vine, it is evident the important deviations in the ratios per hectare. In conclusion, even though this practice can be an option when there is a lack of information, it can lead to important over- or under-estimations that should be considered in the assessment.
  • Literature: whenever no data is available, a usual practice is to pick-up a biomass production rate found in literature (magazines, technical papers, project reports or news releases). Then two aspects must be ensured: 1) the type of work is currently the same. As example,  in case of riverside cleaning, it must be verified which type of operations were executed when obtaining the biomass per hectare: were the workers doing a soft pruning to the trees? Or were they instead cutting down old and damaged trees? 2) The vegetation and ecosystem must be  similar in both cases, the literature referred and the targeted area. E.g. the ratio corresponding to roadside cleaning in very humid climates should not be applied to dry or bare areas.

And what about moisture and bulk density? 

Some additional issues that should be taken into account when inventorying and reporting biomass are the moisture content and bulk density of the material obtained. Some considerations are:

  • Moisture of the biomass which it is obtained might be unknown in many cases, since companies carrying out the work do not measure it. However, depending on the residue, average data could be considered to simplify: 20% for dry grass, 50% for tree living tissues, or 60% for fresh grasses.
  • Bulk densities: many companies executing LCMW treatments only have registered volumes disposed, but not weights. Bulk density of the biomass, that is, the weight per cubic meter of container or truck box, is a parameter to transform the volumes disposed into weight. Bulk density is, however a very uncertain parameter, depending much on the shape and degree of compaction of the biomass obtained. Loose branches on a truck container can have densities from 50 to 100 kg/m3 of truck box. Chopped biomass can range between 150 and 250 kg/m3, whereas wood chips tend to range from 200 to 300 kg/m3.

The figures provided for moisture and bulk density are merely for orientation, and once proceeding with the utilisation step of the biomass, some pilot works must be carried out to better quantify these values, and carry out a realistic assessment of the potentials and the implications of the bulk density for the mobilisation of the biomass.

Step 4: Determine which fraction of the biomass potential can be actually exploited 

The estimations carried out until Step 3 lead to the so called “theoretical potential”. However not the whole potential can be fully exploited in practice. It is therefore necessary to review the inventory and to delete part of the targeted areas:

  • Due to technical constraints: as for example areas of considerable slope for which if the exploitation method requires the use of machinery, some roadside areas will not be able to be harvested with the treatment methods initially foreseen. For determining the technical limitations, it is therefore needed to firstly determine which will be the operational methods and their technical limitations.
  • Due to ownership: as for example private property areas require particular agreements with the owners. If the initiative or operation is carried out by public authorities, those areas might, in principle, not be object of any treatment.
  • Due to regulatory limitations: as for example natural parks which residues are not considered to be utilised for any profitable activity.

Step 5: Pilot experiences monitoring 

Picture 5: Inventorying work for roadside vegetation in Rotenburg (Wümme)

Picture 5: Inventorying work for roadside vegetation in Rotenburg (Wümme)

Pilot experiences should be promoted in agreement with local actors to state and refine the initial assessments, and so, to correct and validate the assessments carried out. Pilot experiences are also quite recommended prior any new biomass supply chain is set up, or previous to any company or authority decides to change its modus operandi. Pilot experiences are crucial since they allow to define the most promising and practical implementation of the LCMW biomass supply chains.

Summary: Reliable assessments for the LCMW biomass utilisation require consideration beyond the theoretical potentials. It is necessary to taken into account the technical, legal and environmental limitations. However, obtaining theoretical potentials is not at all a simple work, as LCMW targeted biomass lacks usually on inventorying and previous assessments. Therefore, data coming from the local reality and from local inventories and sampling is needed as much as possible. Not being based on precise inventories or on precise biomass production rates, the values obtained by LCMW biomass assessments should be always validated through field work and pilot experiences.

Author: Daniel García


FNR - The Agency for Renewable Resources
Christiane Volkmann

CZ Biom - Czech Biomass Association
Jan Doležal

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