Another planting configuration involves an intercropping system using wide rows of sawtimber crops that are interplanted with a biomass crop such as Panicum virgatum. The rows of pine are planted 6.1 m apart and pines are planted 1.5 m apart within each row. To capture the solar energy between rows, a biomass crop is established and harvested for fuel. This dual cropping system has an advantage in that some of the understory vegetation is
|
Table 10.3 An example of the effect of planting additional pine seedlings (base level = O/ha) on the added costs of producing, harvesting and delivering biomass (i. e. extra tonnes) to a biomass plant.
|
Seedlings per ha
|
Yield of green biomass Mg/ha
|
Seedling cost $/ha
|
Hand planting
cost
$/ha
|
Standing value
$/ha
|
Net present value at 5% $/ha
|
Average DBH cm
|
Trees per green Mg
|
Harvest cost per green Mg $/Mg
|
Net present value at roadside at
5%
$/ha
|
|
500
|
111
|
30
|
60
|
3330
|
676
|
23.1
|
3.6
|
10.00
|
676
|
|
1000
|
155
|
60
|
120
|
4650
|
1286
|
19.8
|
5.3
|
11.60
|
1043
|
|
1500
|
179
|
90
|
180
|
5370
|
1578
|
17.8
|
6.9
|
13.10
|
1021
|
|
2000
|
184
|
120
|
240
|
5520
|
1567
|
15.5
|
9.0
|
15.10
|
555
|
|
2500
|
190
|
150
|
300
|
5700
|
1573
|
14.7
|
10.3
|
17.00
|
232
|
|
3000
|
193
|
180
|
360
|
5790
|
1531
|
13.2
|
12.4
|
20.40
|
-476
|
This example involves planting pine seedlings on a site index of 24 m (at 25 years) in the Coastal Plain, a 1 3-yr rotation, a 5% discount rate, an establishment cost varying from $1090/ha to $1 540/ha, a price of $30/Mg for standing trees and $40/Mg for biomass at the roadside. In this example, the optimal planting density for biomass production for this rotation age is 1000 seedlings per ha when including harvesting costs and 1 500 per ha when ignoring harvesting costs.
|
|
Table 10.4 A comparison of a biomass only stand with a hybrid stand (all biomass rows (B) removed at age 14 yr; remaining sawtimber rows (S) harvested at age 24 yr) and a sawlog stand (wide row; thin at age 14 yr; harvest age 24 yr) All data were generated using Ptaeda3.
|
Establishment
|
Biomass only
|
Hybrid stand B Row S Row
|
Sawlog
|
|
Row spacing (m)
|
2.4
|
2.4 2.4
|
4.6
|
|
Spacing within the row (m)
|
2.4
|
2.4 3.0
|
2.4
|
|
Ripping soil ($/ha)
|
250
|
250
|
133
|
|
Machine planting ($/ha)
|
170
|
170
|
91
|
|
Seedling cost ($/ha)
|
84
|
74
|
45
|
|
Herbicide -2m band ($/ha)
|
196
|
196
|
105
|
|
Total cost ($/ha)
|
700
|
690
|
374
|
|
Initial survival (%)
|
89
|
89
|
89
|
|
Stand characteristics at thinning
|
|
|
|
|
Type of thin
|
—
|
Every "B”row
|
Remove small trees
|
|
Live trees at age 14 years before thinning
|
—
|
1243
|
739
|
|
Trees thinned
|
—
|
689
|
460
|
|
Basal area after thinning (m2)
|
—
|
6.2
|
5.6
|
|
Average DBH — cm before thin
|
—
|
17.8
|
21.8
|
|
Average DBH — cm after thin
|
—
|
18.8
|
24.9
|
|
Average height — m before thin
|
—
|
14.7
|
15.7
|
|
gTonnes logs harvested (small + medium)
|
—
|
0
|
30 + 44
|
|
gTonnes of biomass chips harvested
|
|
118
|
0
|
|
gTonnes of branches and tops left on site
|
—
|
0
|
22
|
|
Stand characteristics at harvest
|
|
|
|
|
Rotation age (years)
|
12
|
24
|
24
|
|
Average DBH (cm)
|
17.5
|
26.2
|
33.3
|
|
Average height at harvest (m)
|
12.8
|
21.9
|
25.0
|
|
Trees harvested per ha
|
1391
|
526
|
279
|
|
gTonnes of branches and tops
|
42 harvested
|
39 left on site
|
34 left on site
|
|
gTonnes/ha/yr (including branches)
|
15.6
|
16.0
|
15.4
|
|
dTonnes/ha/yr (including branches)
|
5.9
|
7.0
|
6.4
|
|
gTonnes large (sawtimber/ha)
|
0
|
47
|
193
|
|
gTonnes medium (chip-n-saw/ha)
|
46
|
131
|
3
|
|
gTonnes small (biomass chips or pulpwood/ha)
|
100
|
49
|
45
|
|
gTonnes removed/ha
|
188
|
227
|
241
|
|
Wood properties at harvest
|
|
|
|
|
Average rings per cm (at groundline)
|
1.2
|
1.7
|
1.3
|
|
Specific gravity at harvest (at DBH)
|
0.42
|
0.46
|
0.46
|
|
Basal area in juvenile wood (at DBH) (%)
|
100
|
45
|
28
|
|
Moisture content — (od) (%)
|
138
|
117
|
117
|
|
Number of trees harvested per gtonne
|
8.2
|
2.5
|
1.3
|
|
Mass harvested (24-yr period)
|
|
|
|
|
gTonnes of products (small + medium + large)
|
0
|
227
|
240
|
|
gTonnes of biomass per ha
|
374
|
163
|
0
|
|
Dry tonnes of biomass per ha
|
157
|
68
|
0
|
|
Value of harvested wood
|
|
|
|
|
Biomass — year 12 ($/ha)
|
1692
|
0
|
0
|
|
Biomass — year 24 ($/ha)
|
1692
|
0
|
0
|
|
Biomass or Wood products — year 14 ($/ha)
|
0
|
1112
|
1067
|
|
Wood products — year 24 ($/ha)
|
0
|
4211
|
6182
|
|
Net present value at year zero: at 5% ($/ha)
|
377
|
1177
|
2081
|
Biomass and small logs = $9 per green tonne (gTonne); medium logs = $18/gtonne; large logs = $30/gtonne.
|
converted to a useful product (e. g. a liquid fuel). The company, Catchlight Energy, is currently working with the forest products company Weyerhaeuser in researching the opportunities for producing cellulosic biofuels from biomass crops in pine plantations.
