Utilizing Forest Biomass by Adding a Small Chipper to a Tree-Length Southern Pine Harvesting Operation

Abstract We investigated the addition of a small chipper (Conehead 565) to a mechanized, tree-length system to harvest tops, limbs, and understory (1–4 in. dbh) biomass. Three replicates of three treatments (A, tree-length only; B, tree-length with limbs and tops chipped; and C, tree-length with limbs, tops, and understory chipped) were evaluated in a 33-year-old slash pine plantation on a flatwoods site in the lower coastal plain of Echols County, Georgia. The site contained an estimated 7.7 green tons/ac of understory biomass with an average dbh of 2 in. Water oak, swamp bay, and red maple accounted for 73% of the stems. Roundwood production averaged 65.8 tons/ac and did not differ significantly across the three clearcut treatments. A vanload of chips was produced for every 18 and 5 truckloads of roundwood in Treatments B and C, respectively. There were significant differences in the weight per acre of chips produced between Treatment B (3.8 green tons/ac) and Treatment C (10.8 green tons/ac) at the α = 0.1 significance level but not at the 0.05 significance level. Total production averaged 28.6 tons per scheduled machine-hour and did not differ significantly across the three treatments. Green chips averaged 45% moisture content when produced, and laboratory results showed heat content values of 19.1 MJ/kg, which is comparable to other woody biomass. Nutrient removals from the site were relatively low, with losses associated with Treatment B comparable to annual atmospheric deposition. Raking costs associated with site preparation were significantly reduced (by $23/ac) on Treatment C, where the understory was also chipped. Both Treatment B and Treatment C had significantly less area lost to debris piles (1.0%) after site preparation than tree-length harvesting without chipping residuals (1.7%). Chipping logging residues along with understory stems in a clearcut harvest produced quality energy chips at a competitive cost, reduced site preparation cost, and increased plantable area.