Site productivity impacts of intensified biomass recovery – literature and knowledge review
A new report by Task 43 ( Biomass Supply in a Nature Positive Circular Economy) shows how increasing global decarbonisation efforts are driving demand for forest biomass, with harvesting residues representing the largest untapped opportunity, especially in Australia, where only a small fraction of forest harvest residues are currently used. However, historical evidence from aggressive “clear and burn” site (re)establishment practices shows that removing most above-ground biomass can severely damage long-term site productivity, especially on nutrient-poor soils, and this has made managers cautious about pursuing intensive biomass recovery today. With limited clarity on how much harvest residue can be removed without degrading future site productivity, the project aims to review the global evidence on short and long-term site productivity impacts at different levels of biomass recovery, and outline a future research agenda to identify critical thresholds and equip plantation managers with the knowledge needed to supply biomass at scale while maintaining sustainable site productivity.
The impact of harvest residue removal has only been studied in detail for a limited range of tree species, predominantly in the northern hemisphere. Strong evidence was found that removing most harvest residues can reduce site productivity for some studied species, especially Norway spruce, where growth declines have been observed on both low and high-fertility sites, and for several eucalypt species, particularly, on low fertility sites under repeated short rotations with repeated residue removal. In contrast, species such as Scots pine, Lodgepole pine and Radiata pine appear more tolerant to harvest residue removal, possibly due to superior nitrogen-use ability. The authors emphasise that the effects of harvest residue removal are highly context-dependent, interacting with species, soil, silviculture, and climate and, that much of the literature is based on unrealistically high levels of harvest residue removal (often total removal) compared with real-world practice, where around half the harvest residue is retained onsite. Limited studies on partial residue removal show little or no growth loss, pointing to a major evidence gap. Further research is needed into how typical operational residue retention levels, nutrient compensation via fertiliser, and nutrient dynamics within deeper soil layers affect site productivity throughout rotations.
Key findings:
- Retain caution on high levels of biomass-residue removal: Policies that promote aggressive biomass recovery from forest harvesting should recognise that on low fertility sites (or for sensitive species) removal of large proportions of logging residue may undermine long-term site productivity and hence forest sustainability.
- Avoid one‐size-fits‐all: Residue-retention rules should reflect local site fertility, tree species, rotation length and management regime. Policy should support development of indicators for safe levels of forest biomass‐retention to maintain site productivity rather than prescribing fixed minimum retention levels across all forest types and sites.
