Abstract
The utilization of forest harvest residues for renewable bioenergy production and bioproducts has increasingly become an integrated part of forestry that helps to meet the needs of climate change mitigation and a future carbon neutral economy. An essential element in the planning of any harvesting residue recovery operation is a reliable assessment of the quantity and quality of residue biomass and its composition over a harvest area. With the now widely adopted cut-to-length (CTL) at the stump harvesting system in Pinus radiata plantations in Australia, harvesting residues left on site are significantly larger in quantity and spatially more dispersed over a harvest area in comparison to the more traditional whole-tree harvesting. The conventional approach of assessing forest harvest residues through sample plots, transects, or small study blocks has provided site-specific estimates of residue biomass. However, these estimates cannot be readily extrapolated over the plantation landscape, which varies in silviculture, site, and stand conditions. To overcome this limitation, this study relied on harvester data analytics to obtain spatially explicit estimates of residue biomass using an example data set from harvested plantations of three stand types: unthinned (T0), thinned once (T1), and thinned twice (T2). Three methods of integrating biomass equations with harvester data were compared for residue biomass estimation: (1) applying individual tree biomass equations to harvested stems, (2) applying stand-level biomass equations to gridded harvester data, and (3) integrating estimates from the first approach with recorded and estimated waste volumes of harvested stems. The estimates of total residue biomass obtained using the three methods through harvester data analytics varied between 56.2 and 156.4 t/ha in green weight across the three stand types. These estimates were validated indirectly through ex situ sample plots and proved to be comparable to the quantities of residue biomass assessed using conventional sample plots, transects, or small blocks following CTL harvesting of rotation age P. radiata plantations elsewhere in Australia. Among the three methods, the third method made the most intensive use of the harvester data and provided the most realistic estimates of residue biomass. Spatial mapping of the estimated total and component residue biomass will assist the operational planning of residue recovery and site-specific nutrient management for the long-term sustainability of P. radiata plantations.
Highlights
The utilization of forest harvest residues in managed forests for the production of renewable bioenergy and bioproducts has increasingly become an integrated part of forestry that helps to meet the needs of climate change mitigation and a future carbon neutral economy [1–10]
This study aimed to introduce harvester data analytics for the estimation and spatial mapping of residue biomass in plantations following CTL harvesting and to demonstrate the usefulness of this novel approach in overcoming the limitations of the conventional inventory and sampling-based residue biomass estimation
Pinus radiata plantations are a major source of harvest residue biomass for renewable bioenergy production in Australia
Summary
The utilization of forest harvest residues in managed forests for the production of renewable bioenergy and bioproducts has increasingly become an integrated part of forestry that helps to meet the needs of climate change mitigation and a future carbon neutral economy [1–10]. The harvest residues mainly consist of stumps, branches, and treetops, as well as short offcut and waste sections due to stem deformity, defects, damage, and breakage. They may include standing broken stems and standing dead trees if left unharvested. With the widely adopted cut-to-length (CTL) at the stump harvesting system, residues left on site are significantly larger in quantity and spatially more dispersed over a harvest area in comparison to the more traditional whole-tree harvesting, whereby trees are delimbed and bucked at the landing site [12,14,15]. In addition to providing environmental benefits, residue recovery following CTL harvesting would reduce the intensity of post-harvest residue management and thereby minimize the cost of site preparation for the rotation, where residue levels are high [11,16,17]
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