Combining slash bundling with in-woods grinding operations

2004). Forest operations have the potential to supply 368 million dry tons of woody biomass
annually (Perlack et al. 2005). The annual available biomass in California was estimated at 26.8
million dry tons (Tiangco et al. 2005). Prescribed burning has long been the preferred method of
disposing of forest biomass, but mechanical removal of biomass is becoming more popular due
to increased restrictions on open field burning, or in areas like the wildland urban interface
(WUI) where burning is not an option.
Forest residues are often not utilized because collection and transportation costs are greater than
the market value of the materials (Withycombe 1982). Lack of research in this field has made
harvesting and transportation costs are notoriously difficult to estimate because there are critical
gaps in the data and methods for predicting costs (Rummer et al. 2008).
New, more efficient harvesting equipment like energy wood harvesters could reduce the
associated processing costs with their increased productivity. These machines compact and
bundle woody biomass into log-shaped bundles, and could produce up to 40 half-ton bundles per
hour with a production cost of $16 per dry ton (Rummer et al. 2004). Quantifying costs and
productivities of these new systems for biomass recovery from northern California will aid land
managers in the planning and execution of cost-effective biomass supply for energy.
The overall objective of this project was to determine the operational cost and performance of a
biomass collection and densification system, called slash bundler, in combination with a
centralized grinding operation. Important variables, such as hauling distance and moisture
contents, were itemized to understand their effects on productivity of collection and
transportation. In particular, slash piles were characterized to evaluate the effect of slash type on
productivity, based on arrangement and size of slash materials.
Methodology
Study site and system description
The study was conducted in three clearcut harvesting sites in northern California, ranging from
17 to 32 acres. The vegetation at each site varied but was generally dominated by second growth
redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga menziesii) with an average tree
age of 60 years. The three sites had an average tree diameter at breast height (DBH) ranging
from 20-22 inches, and ground slopes ranged from 0 to 30 percent. The stands were harvested
using a ground-based shovel logging system. There were many slash pile types in terms of size
and arrangement present across these sites (Fig. 1). A forester working for the land owner
suggested these sites were expected to yield anywhere from 50-75 tons/ac of slash from clearcut
operations (Alcorn 2008).