DOI: 10.5061/dryad.qv9s4mwg7
title: Bark content variations and the production of Populus deltoides as a source of bioenergy under temperate climate conditions

description: Bark biomass as an energy source has a high economic value. Bark content
 variations and production helps recognize the potential of this bioenergy
 source spatially before harvesting. The percentage of fresh and dry bark
 in Populus deltoides grown under a monoculture system
 was examined in the temperate region of northern Iran. Diameter at breast
 height (DBH) and total height data were analyzed based on an initial
 inventory. Ten sample trees were felled, separated into
 2 m-segments, and weighted in the field. A 5-cm-thick disc from
 each segment was extracted for determining fresh and dry bark percentages.
 These were statistically significantly different in disc diameter classes
 and decreased with increasing disc diameters. Bark percentage of the disc
 classes ranged from 21.8 to 24.4% in small-sized diameters to 8.1‒9.3% in
 large-sized diameters. The differences between fresh and dry bark
 percentages depended on water content variations. Allometric power
 equations were fitted to data of fresh and dry bark percentages and disc
 diameters as well as DBH. The values of R2 ranged from 0.89 to
 0.90. In addition, allometric power equations provided the best fits for
 relationships between total stem dry biomass, dry bark biomass, and
 DBH, R2 = 0.986 and 0.979 for the total stem dry biomass and stem
 dry bark biomass, respectively. The allometric models can be used to
 estimate bark percentage and bark production of P. deltoides in
 segments and for the whole stem for a wide range of segment diameters
 (8‒44 cm) and DBH (15‒45 cm).
description: Plot design and harvesting <br>Twelve
 sampling plots (16 m × 16 m) in three P. deltoides plantations were
 established based on systematic random design. To minimize edge effects,
 surrounding rows were not considered during sampling. The age of the
 stands was 18-20 years old. In each sampling plot, the DBH (diameter at
 breast height 1.3 m above the ground) of the individual trees was measured
 with a caliper in two perpendicular directions and the mean DBH
 determined. Tree height was measured by Haglöf-Vertex IV hypsometer. Based
 on the DBH and height measurements, 10 DBH classes from 15 to 42 cm (3 cm
 intervals) were established. The value of each DBH class represented the
 central value (i.e., class 15 included all DBH from 12.5 to 17.5 cm). In
 each DBH class, one representative tree was selected and harvested for a
 total of 10 P. deltoides trees. <br><br>Measurements of bark
 percentages<br><br>The stems of harvested trees were marked
 and cut into 2 m-segments. The mid-length diameter of each segment was
 measured outside the bark in two perpendicular directions with a caliper
 to determine the mean diameter. A 5 cm-thick disc was cut from the middle
 of each segment. A total of 123 discs were obtained and brought to the
 laboratory. All the discs were arranged into 2-cm wide diameter classes.
 The value of each disc class represents the central value (i.e., class 20
 included all discs whose diameters ranged from 19.5 to 20.5 cm). Bark was
 separated from the wood using a peeler knife for each disc. Fresh bark and
 wood were weighted separately, oven-dried at 80 °C until constant weight,
 and the oven-dry weight measured. The bark percentage of each disc was
 considered as bark percentage of a 2 m-segment for fresh and dry weight.
 Finally, the bark percentage of the whole stem in each DBH class was
 calculated by adding the 2 m-segments.