Herbivory Protection

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National Park Service

Herbivory can cause mortality of revegetation plantings. All strategies to reduce herbivory consume resources. Herbivory pressure can change with the season, among locations and from year to year.

All unattributed comments are pulled off the WesternWARiparianWorkGroup listserve.

Beavers

  • On our beaver sites we are relying on beaver fencing (very expensive) or planting at high densities. I have noticed in our reed canarygrass plantings where we plant stakes at 3-foot spacings (5000 plants per acre), beaver damage has been limited to small areas that I can live with. Whereas when we plant 500 stakes per acre the beavers destroy several acres of plantings.
  • We tried planting our trees with a paint/sand mixture to no avail.
  • We are beginning to experiment more with planting sites with more beaver-resistant varieties, like Pacific ninebark (Physocarpus), twinberry (Lonicera), and hardhack (Spirea). I generally do not see beaver harvesting ... (there are probably a few others), at most sites. So, perhaps a shift to less beaver-palatable species is in order.
  • I think the Skagit Conservation District has also found Oregon ash to be fairly unpalatable. In one stand that was totally wiped out by beaver Oregon ash was the last tree standing.
  • I have observed sites where beavers apparently walked through a wall of willow (Salix) and dogwood (Cornus) over 25’ from the creek just to crop-off a planted 4’ tall cedar (Thuja) in the early spring. You then find the cedar stem completely debarked in the creek—so it’s a food thing.
  • I used to have good luck with Red Osier Dogwood (Cornus) and rarely found them browsed but sound like from Derek that dynamic has changed. I also rarely had big leaf maple browsed. A lot of older spruce out there that have survived the gauntlet.

Voles

  • The following comments are pulled off of the WesternWARiparianWorkgroup, and generally reflect an assumption that tree protectors are the primary method.
    • "We are currently using biodegradable, mesh plant protectors. At first we tried 2% biodegradable additive and the protectors broke down before the first summer. We lost around 4 acres of plants to voles that year. Now we are using 0.25% additive and the protectors last around 3 years. What are other people using? Has anyone decided it is more cost efficient not to use protectors at all?"
    • "Folks doing industrial tree farming commonly spray to bare ground around the trees to deter voles. This is supported in some research, although no one is excited about more chemical use. https://www.fas.scot/downloads/tn690-protecting-young-woodlands-vole-damage/"
    • "This paper also mentions slash piles for predator habitat. Another idea is perch poles for raptors. These are in use at some local tree farms as well. We plan to install some in field conversion projects this year where there is no adjacent canopy. I've seen 1 per acre as a metric."
    • "Importantly, plastic tubes break down into smaller pieces and often get into waterways. Regardless of photo-degradation duration, they are rarely removed entirely. Here’s a link to a recent story on microplastics in the Columbia. "
    • "weedeaters in untrained hands have killed more trees that beaver or voles. The plant protectors have been the best defense"
    • "Europeans are way ahead of Americans by using compostable tubes instead of blue plastic tubes."

Deer/Elk

  • We are using a combination of spruce (Picea)/cedar (Thuja) companion plantings and Plantskydd repellant.
  • A study we did at Savage Slough showed both significantly reduced browse and that has proved true across our sites. We apply Plantskydd to our deciduous plants twice during the winter when the elk are in the lowlands and grass is not growing as much. The second application is timed right before bud break.
  • We are also burying our protectors 1.5-feet into our holes when we plant to prevent removal by elk.
  • Watershed Company 2021 describes effectiveness of PlantSkydd and blue tubes in controlling deer browse.
  • Symphoricarpos, Corylus and Holodiscus appear less heavily browsed in some settings.
  • Planting vulnerable plants into loose slash piles can prevent ungulate access and allow survival.