The Role of Herbicides in Logging Site Preparation

Fire damaged pines amongst regrowth
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Reforestation is vital to restoring harvested trees and revitalizing landscapes after natural disasters such as wildfires and droughts. Making the reforestation process more efficient and maximizing the chances for seedlings to succeed helps accelerate the restoration of landscapes and, in areas used for commercial logging, lays the groundwork for future healthy harvests.

In California, the 2012-2016 drought killed an estimated 129 million trees in the Sierra Nevada.1 Meanwhile, wildfires are becoming more intense and frequent, making reforestation even more difficult. In some cases, fires consume trees that had only recently been planted to reforest from a prior fire. With smaller staffs and tighter budgets, public land management agencies also need reforestation strategies that allow them to do more with less and can ensure a high rate of success without a lot of repeat visits or “course corrections.”1

For commercial growers and timber harvesters, many of the challenges of other sectors of agriculture apply. Forest land available for harvest is shrinking. Producers need to be able to maximize volume from their harvests with practices that promote high survivability of seedlings and faster tree growth.

One of the biggest challenges in replanting areas is managing competing vegetation. When used as part of an integrated vegetation management (IVM) approach, herbicides can be highly useful and cost-effective tools in creating optimal conditions for conifer seedlings to take root.

Benefits of controlling competing vegetation

Once transplanted, anywhere from 5-50% of seedlings may die.2 That means each seedling placed in the ground needs all the resources it can access in order to succeed. Competing vegetation, including grasses, shrubs, forbs and hardwood trees, consume those valuable resources—especially water. In already dry conditions, grasses in particular can take up moisture young trees need, potentially worsening drought stress.3

Controlling competition improves seedling survival, which reduces reforestation costs. It also accelerates tree growth, resulting in faster crown closure. That increases forest stand development and can help increase timber production. Addressing grass competition also helps reduce populations of voles and pocket gophers, which can damage and kill seedlings.3

If seedlings can’t survive and grow, the landscape risks falling into a vicious cycle as more competing vegetation moves in where trees fail to thrive. In order to improve seedling survival rates and promote growth, competition should be reduced to 30% or less. Researchers note that, “even small increases in competition can result in large losses in growth.”3

4 ways herbicides can help

  1. Fostering faster growth and improved yields
    Decades of research have shown that using herbicides to control competing vegetation benefits tree growth and timber yield. This is vital for the timber industry, as it works to meet the world’s demand for wood and also fulfill reforestation requirements for trees harvested. A review of numerous studies of the use of herbicides in reforestation efforts showed herbicides can help increase wood volume, enabling yield to increase anywhere from 30-300% in a range of site conditions across the U.S.4 For land managers working to restore areas damaged by drought or wildfire, faster growth enables a more efficient rehabilitation of the landscape and can add to wildfire resiliency.
  2. Aiding in conifer release
    Trees need adequate moisture and sunshine to get off to a strong start after planting. Competing species can take up these resources, reducing establishment by as much as 70%. Herbicides that are safe for use over tree seedlings help control competing brush and weeds, and don’t require trees to be shielded during application. Choosing herbicides with good residual control can also reduce the need for follow up treatments, saving time and labor.
  3. Protecting a critical period of growth
    The first one to two years after planting are critical for seedling establishment. Herbicides used during this phase can help reduce weedy competition.5 Here again, herbicides with good residual control can be particularly valuable, allowing areas to remain weed- and brush-free for as long as two years, protecting trees during this vulnerable time without the need for repeat treatments that would require land managers to spread already limited resources thin.
  4. Maintaining biodiversity
    Use of selective herbicides—which target only specific plants—also helps maintain biodiversity in forest areas. This can lead to enhanced wildlife habitat6 as well as promoting native vegetation. More biodiverse environments become more naturally self-sustaining and have features such as lower-growing, less flammable vegetation that make forests more resilient in the face of wildfires.

Choosing the right herbicides to support reforestation

Whether replanting after timber harvest or to restore lands after wildfires, foresters and land managers have choices in herbicides for preparing sites and ensuring good conifer release. It’s important to look for herbicides that offer tree safety, convenience, lasting control and selectivity, so the landscape can return to its naturally biodiverse state. Cleantraxx® herbicide is one option foresters are turning to for site preparation. Cleantraxx delivers two modes of action for preemergence control of broadleaf weeds, annual grasses and certain woody brush seedlings, with up to six months of residual control. Cleantraxx offers excellent conifer safety and can be applied from pre-bud break to early post-bud break in several key species including Ponderosa pine, Douglas fir, western larch, white fir, sugar pine, redwood and incense cedar. It also carries a Special Local Needs (SLN) label for use in California, Oregon, Washington and Idaho forestry. For more complete broadleaf control, Cleantraxx can be mixed with Transline® herbicide, which is highly selective, and safe over many species of conifers, hardwoods and warm and cool-season right-of-way grasses. Transline is rainfast within two hours and, like Cleantraxx, offers excellent residual control over invasive, noxious weeds, including infestations around pine trees. Its tank-mix compatibility and low volatility also make Transline convenient to use.

Demonstrated residual control and conifer tree safety7


Approximately one year after treatment with Cleantraxx, the area around these seedlings  remains clear of competing weeds and brush.


A view of incense cedar, sugar pine and Ponderosa pine seedlings one year after Cleantraxx was applied at post-bud break. The trees are growing normally with no signs of herbicide injury.

Whether valued for their commercial potential, natural beauty or both, forest lands are among our nation’s most important natural resources. They’re also among our most challenged, facing threats every year from climate, fire, human activity and invasive and noxious vegetation. Restoring these lands and keeping them flourishing is vital to our economy and the ecosystem. With an IVM approach, including responsible use of herbicides, foresters and land managers can give young trees their best chance at growing tall and strong and continuing the cycle of renewal in these treasured landscapes.

References

1 Malcolm P. North et al., “Tamm Review: Reforestation for Resilience in Dry Western U.S. Forests, Forest Ecology and Management 432 September 21, 2018): pp. 209-224, https://doi.org/10.1016/j. foreco.2018.09.007.
2 Allison Guy, “Growing Pains: The Race to Plant Billions of Trees,” (American Forests, October 5, 2020),  https://www.americanforests.org/article/growing-pains-the-race-to-plant-billions-of-trees-2/.
3 Paul Oester and Stephen A. Fitzgerald, “Enhancing Reforestation Success - OSU Extension Catalog” (Pacific Northwest Extension, February 2016), https://catalog.extension.oregonstate.edu/sites/catalog/files/
project/pdf/pnw520_6.pdf.
4 Robert G. Wagner et al., “The Role of Herbicides for Enhancing Forest Productivity and Conserving Land for Biodiversity in North America,” Wildlife Society Bulletin 32, no. 4 (2004): pp. 1028-1041, https://www.
fs.usda.gov/research/treesearch/8975.
5 John Greene, “Sowing What You Reap: Replanting after a Timber Harvest” (Forest2Market, January 11, 2022), https://www.forest2market.com/blog/sowing-what-you-reap-replanting-after-a-timber-harvest.
6 David R. Jackson and James Finley, “Herbicides and Forest Vegetation Management” (Penn State Extension, September 14, 2007), https://extension.psu.edu/herbicides-and-forest-vegetation-management.
7 Corteva Agriscience. Field observations. Data on file.

When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product labels for details. State restrictions on the sale and use of Transline® apply. Consult the label before purchase or use for full details. Cleantraxx® is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Always read and follow label directions.