Canadian Forest Service Publications
Effect of vegetation control, harvest intensity, and soil disturbance on 20-year jack pine stand development. 2018. Fleming, R.L.; Leblanc, J.-D.; Weldon, T.; Hazlett, P.W.; Mossa, D.S.; Irwin, R.; Primavera, M.J.; Wilson, S.A. Canadian Journal of Forest Research 48:1-17.
Issued by: Great Lakes Forestry Centre
Catalog ID: 39058
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Currently, there are uncertainties regarding the impacts and (or) efficacy of biomass harvesting and silvicultural practices on stand production on coarse-textured boreal soils. Replicated factorial field experiments examining effects of complete vegetation control (repeated glyphosate application) following operational stem-only harvest with disc trenching (SOT), operational whole-tree harvest with (WTT) and without (WT) disc trenching, and whole-tree harvest with complete forest floor removal by blading (WTB) and blading followed by compaction (WTBC) were installed on four sandy northern Ontario jack pine (Pinus banksiana Lamb.) sites. Over 20 years, WTB improved planted-tree survival but decreased longer term stand productivity in comparison with other harvest intensity – soil disturbance treatments. Vegetation control improved tree growth and stand productivity initially, but over time, benefits declined substantially. SOT andWTT had similar impacts on stand production. Disc trenching improved initial planted-tree growth (WTT vs. WT), particularly without vegetation control. Jack pine natural regeneration was greatest with SOT, accounting for 25% of stand biomass at year 20. Stand structure effects included increased size inequality of naturals with WTB and reduced size inequality and asymmetry of naturals with vegetation control. Overall, impacts of forest floor removal and natural regeneration on stand development have become increasingly important over time compared with those of vegetation control.
Plain Language Summary
This paper examines 20 yr. jack pine stand growth response to whole tree harvest, stem-only harvest, disc trenching, complete forest floor removal (blading) and compaction following blading, each with and without repeated vegetation control (glyphosate applications). The experiment was individually replicated on four sites on infertile coarse-textured soils with shrub and herb-dominated understory vegetation in northeastern Ontario. Key findings were: 1) complete forest floor removal slightly increased planted tree survival but reduced longer-term stand productivity; 2) vegetation control markedly increased stand growth initially but effects lessened substantially over time; 3) whole tree harvesting had similar effects on stand development as stem-only harvesting; 4) compaction following forest floor removal had no additional effects on stand development; (5) ingress of natural regeneration was greater with harvest/site preparation treatments that maintained cone-bearing logging slash on-site, but was not significantly affected by vegetation control. The importance of this publication lies in the longer-term (20 yr.) responses it reports. Forest floor removal on similar sites is likely to have substantial negative impacts on longer-term stand productivity despite showing little evidence of this in the short term. By contrast, positive vegetation control effects on future stand productivity of similar site types can be substantially overestimated when based on short-term results. At this point there is also no strong evidence that operational whole-tree harvesting, as was practiced on these sites, reduces stand productivity compared with stem-only harvesting.