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Understory Retention: Two-Stage Mixedwoods Harvesting Approach

This management approach focuses on establishing a stratified mixture of understory vegetation through underplanting, while retaining the existing understory during harvest. The strip shelterwood method is used to protect the retained spruce from blowdown, ensuring continuous forest cover and maximizing future volume. Underplanting helps maintain mixedwood abundance and provides various benefits, including reduced damage and costs, increased thermal cover, and continuous forest cover.

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Understory Retention: Two-Stage Mixedwoods Harvesting Approach

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  1. Understory Retention at harvest Two stage mixedwoods Establish a stratified mixture Underplanting Establish & or protect understory Sw Clearcut, establish Sw and leave • Harvest aspen , • release understory spruce and • harvest aspen / spruce at 120-140 years

  2. Understory Retention at harvest Two stage mixedwoods Establish a stratified mixture Underplanting Clearcut, establish Sw and leave

  3. Strip Shelterwood Harvest Method

  4. Example of a Management Approach • If aspen stand to be harvested has a spruce understory which is projected to produce > 125 m3/ha at rotation then the spruce would be protected during harvest • Strip shelterwood / 2 stage harvesting model • - aspen windbuffers protect retained spruce from blowdown • - aspen regenerates in openings around released spruce but does not overtop

  5. Strip ShelterwoodUnderstorey retention Projected Understorey Stands using TASS • Pre-harvest conditions • 1600 spruce per ha • 12m spruce top height

  6. Projected Volume and Trade Values Top ht = 12m Top height tpha Existing Sw understory trees / ha Projected future volume - includes estimates of harvest damage

  7. Strip ShelterwoodUnderstorey retention Projected Understorey Stands using TASS Post harvest conditions Reductions to spruce: • - 20% of area - roadside processing • - 22% trails • - 8% blowdown / damage Expect that all healthy Sw greater than 5 m tall will keep pace with the At

  8. Strip ShelterwoodUnderstorey retention Projected Understorey Stands using TASS Age 80 • CD stand • Conifer volume : 217 m3 At regenerating on trails / roadside processing areas

  9. Understory Retention at harvest Two stage mixedwoods Establish a stratified mixture Underplanting Clearcut, establish Sw and leave

  10. Benefits of Underplanting • May help to maintain / increase abundance of mixedwood • Decreased incidence of : • frost damage • overwinter injury • certain types of insect attack • Sw root rot • Decreased site preparation / weeding costs • Ungulate thermalcover • Continuous forest cover 17 year old underplant R.Kabzems

  11. Underplanting cont’d • Reducing hare damage • do not underplant when hare cycle is on the increase • avoid underplanting in close proximity to dense young aspen stands or dense Sb stands • underplant in the interior of extensive mature aspen stands to avoid hare damage

  12. Underplanting …cont’d • Planting density & distribution can be adjusted to target stand objectives • patches or even distribution • high or low density • strips to reduce damage when At is harvested • Selected stands should not have heavy understory competition(understory layers carry more leaf area than overstory)

  13. Understory Retention at harvest Two stage mixedwoods Establish a stratified mixture Underplanting Clearcut, establish Sw and leave

  14. Plant Sw at 1400 spha treat only as required to establish Accept aspen densities low light environment for Sw slow growth set up for 2 stage harvesting model Establish Sw & Leave

  15. Survival for plant & leave Approximately 10 000 Aspen on planted mound

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