Utilizing forest biomass by adding a small chipper to a tree-length southern pine harvesting operation.

摘要

We investigated the addition of a small chipper (Conehead 565) to a mechanized, tree-length system to harvest tops, limbs, and understorey (1-4 inches diameter at breast height (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 understorey chipped) were evaluated in a 33-year-old slash pine (Pinus elliottii) plantation on a flatwoods site in the lower coastal plain of Echols County, Georgia, USA. The site contained an estimated 7.7 green tonnes/ac of understorey biomass with an average dbh of 2 inches. Water oak (Quercus nigra), swamp bay (Persea palustris [Persea borbonia var. pubescens]), and red maple (Acer rubrum) accounted for 73% of the stems. Roundwood production averaged 65.8 tonnes/ac and did not differ significantly across the three clearcut treatments. A van-load 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 tonnes/ac) and treatment C (10.8 green tonnes/ac) at the alpha =0.1 significance level but not at the 0.05 significance level. Total production averaged 28.6 tonnes/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 understorey 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 understorey stems in a clearcut harvest produced quality energy chips at a competitive cost, reduced site preparation cost, and increased plantable area.