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MATERIALS 55
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Species Management Stem Age Acronym cycles were monitored by maintaining a variable temperature
Beech Coppice 30 beech30 range between 60 and 100 deg C.

Beech High forest 70 beech70 For the evaluation of pellet quality, we focused on those
Turkey oak Coppice 20 oak20 parameters that generally represent the major challenges for
Turkey oak Coppice 25 oak25 producing high-quality pellets from feedstocks other than
Eucalyptus Short Rotation Coppice 3 euc3 softwood sawdust, namely bulk density, lower heating value,
Eucalyptus Medium Rotation Coppice 6 euc6 and ash content.
Eucalyptus Coppice 18 euc18 For all the parameters, we referred to the specific standards
Poplar Short Rotation Coppice 3 poplar3 for their determination. Bulk density was assessed directly after
Poplar Medium Rotation Coppice 6 poplar6 the pellet production with a 0.005 cubic metre container, filled
Poplar Coppice 9 poplarg and weighed with a 0.01 precision scale, and 50 replications
per pellet type were carried out.
Preparation & Quality Assessment Lower heating value was assessed by a calorimeter Anton

All the investigated types were derived from harvesting Paar 6400 (Moline, IL, USA), and 50 measurements per pellet
interventions carried out with the whole tree system, therefore type were carried out. Ash content was assessed using a
all the base materials for preparing the pellet contained a muffle furnace (Lenton EF11 8B, Hope Valley, UK) at 250
certain percentage of bark, branches, and leaves. deg C for one hour and at 550 deg C for two hours; also, in
Following chipping, the biomass was refined using a BL- this case, 50 measurements per pellet type were performed.
100 shredder fitted with a grid with 6 mm holes. The proposed statistical approach is based on the
Following reduction, we placed the various biomass types calculation and further summarisation of the effect size, namely

in bins and occasionally exposed them to the sun to speed the standardised mean difference expressed as Cohen’s d.
up the dehydration process until they reached the appropriate Te Linear Mixed-Effects Models (LMMs) fitted by Restricted
moisture level (about 10%). Maximum Likelihood (REML) was used to calculate the 95
We then proceeded to pelletise the biomass. Pelletisation percent confidence intervals for the effect size and the influence
was carried out at two different sites with two different machines, on species, stem age, and pellet type.
a four kW Bianco Line (Cuneo, Italy) and a 5.5 kW Ceccato A mixed-effects approach was used considering that
(San Giorgio delle Pertiche, Italy). the production of pellets with two different machines could
It is worth highlighting that the methods and procedures represent a source of data nesting. We therefore indicated
for producing the pellets were exactly the same in both the in the model the machine used for pellet production (Bianco

sites, only the machine was different. Line or Ceccato) as a random effect. We fitted an
In detail, we reported the technical data for the two LMM for every single independent variable (bulk density,
pelletizers as follows: maximum production capacity of 60–70 ash content and lower heating value), indicating the species
kg/h; six mm flat die model for the production of pellets with and stem age as fixed effects with the lme4 package in R
a length of 30 mm (±5 mm). 4.3.1 software.
Before production, the pelletisers were warmed up to Then, we further fitted LMM for every variable indicating
an optimal temperature of 70 deg C. Once the optimum the pellet type as fixed effect. We used the packages ggeffects

temperature was reached, indicated by the outflow of durable and emmeans o calculate and visualise the marginal response
pellets, the production of samples started. The production and marginal means representing the mean values of each