Welcome to the first post in our new series about best practices in ecological restoration. Through this series we hope to provide an accessible but thorough outline of the most important elements of implementing ecological restoration projects. Nearly everything to do with ecological restoration is complex, and there is still a lot of research being done into best practices, so it is important to keep an eye open for new information. Our goal is to outline the basics, and point you in the direction of more detailed information if you choose to go in depth on any topics.
We are starting our ecological restoration best practices series with a focus on site preparation. The importance of site preparation is often underestimated but can have a huge impact on the success of your restoration project. If you would like to go more in depth into a range of site preparation issues, we highly recommend the Xerces Society “Organic Site Preparation for Wildflower Establishment” document.
The time of year that you choose to disperse native plant seeds at your restoration site is extremely important. Native plant seeding usually happens either in the fall or spring in the Pacific Northwest. In Southern Oregon, fall is generally the best time to get seeds in the ground, as it gives time for in-ground stratification (cold treatment) and mimics the seeding cycles of most native plants. Early spring can also be a hard time to do site preparation if the ground is too wet, or covered in snow! But spring seeding is still a good option if site preparation is possible and the seeds you are using don’t require a deep winter stratification.
Planting potted native plants is generally best done in the fall to provide time for settling and root growth, but early spring is an option if the ground is not too frozen and supplemental water can be provided if spring rains are not sufficient.
Surveying Your Site
Recording the plants that already exist on your site is a great opportunity to better know the plants, their needs, and ways the native plants can be protected during the site preparation phase of your project. You can just write down a list in a notebook, or keep a spreadsheet where you can update information about shifts in flowering, seeding and other interesting observations you make. It’s also a really good idea to keep a record of any weeds you can identify and get to know their lifecycles, best times of year to work on removing them, and the best practices for how to reduce their impact on your restoration site.
Inadequate weed suppression can have massive impacts on the success of your ecological restoration project. For most weeds, an important control method is removing or cutting back the plant before it goes to seed. Different weed plants tend to require a variety of removal methods, used in progression. Some of these methods include solarization and sheet mulching, mowing, flame weeding or burning, and selective and careful herbicide (incl. organic) use. To dive further into best practices for removing some of our most detrimental weeds in Southern Oregon, check out these documents:
- Yellow Starthistle Management Guide
- Field Guide for Managing Yellow Starthistle in the Southwest
- Controlling Himalayan Blackberry in the Pacific Northwest
- Managing Himalayan Blackberry in Western Oregon Riparian Areas
- Rogue Weeds: Garlic Mustard
- Invasive Knotweeds
Solarization and sheet mulching: these methods are best used for smaller sites without steep slopes. Solarization utilizes large sheets of clear UV-stable plastic to cover an area containing weeds for 2-6 months in warmer climates, and up to 6 months in colder climates. Many trials have shown solarization to be an extremely successful method of weed removal, as the heat that builds up under the plastic not only kills plants, but also any weed seed bank that has built up in the soil. Occultation is a variation on solarization, where thick black plastic tarps are used to cut of access to sunlight, and produce large amounts of heat. Sheet mulching is useful in areas that are too shady for solarization to be effective, or in areas where laying out a large piece of plastic is impractical due to landscape features. Sheet mulching involves layering nitrogen and carbon based materials to smother weeds and stop the seed bank from being able to germinate. For example, a layer of nitrogen-based material (eg. animal or plant composted materials, pellets, meals, grass clippings) is then topped with a layer of carbon-based material (eg. cardboard, paper, sawdust, woodbark), and then these layers are repeated 1-2 more times, making sure that a heavier carbon-based material is on top to hold everything down.
Mowing: this can be a very useful tool in ensuring a weed population doesn’t get to produce seed. For most weeds, using a mower or weed wacker to remove any seed heads before they -are pollinated is a fast and efficient way to deplete the plant’s ability to reproduce. That said, it can be hard to time mowing so that the plant doesn’t have the time and energy to enter into the flowering stage again, while also navigating any fire season restrictions on cutting dry grass. This method involves getting to know your weeds and their reproductive cycle well, and should be used in tandem with other weed control methods.
Fire: flame weeders are an excellent resource for spring-time weed control. They must be used with great caution and attendance to fire restrictions, but they are an efficient and targeted method for removing weeds without impacting surrounding native plants. If you have a large area that would benefit from prescribed fire, get in touch with your local prescribed fire practitioners to see if there are any opportunities available for this work to be done on your land by trained professionals. In Southern Oregon, The Klamath Siskiyou Oak Network may be able to point you toward prescribed fire resources.
Smother cover crops: in areas where weed pressure is low to moderate, cover crops can be used to smother weed plants. Smother cover crops can also improve soil health and provide temporary forage for wildlife, including pollinators. This technique is best used on farmland or pasture that has access to irrigation and farming equipment. Certain varieties of buckwheat, sorghum, millet, oats, rye and vetch can be planted. Depending on the cover crop planted, they can not only compete aggressively with weeds for space, but also alter the nutrients in the soil and release allelopathic substances into the soil to make it undesirable for weed germination and growth. Timing and duration of the cover crop also varies depending upon species, but is very important to ensure that weed suppression is maximized.
Herbicides: using synthetic herbicides to control weeds is a very contentious issue, but best practices generally determine that they should be used as a last resort, and in a very targeted and well-planned manner. This is particularly important in riparian zones where herbicides can make their way into the aquatic ecosystem. Herbicides alone are rarely able to control the most problematic weeds, and should be considered part of a regime that involves other weed control methods. There are some organic herbicides available to use, and successful use depends on targeted plant species. For more information it is worth checking out the “Roadside Habitat for Monarchs: Monarch Butterflies, Weeds and Herbicides” and “Organic Pesticides: Minimizing Risks to Pollinators and Beneficial Insects” documents produced by the Xerces Society.
If you are utilizing native seeds in your restoration project, gentle ground disturbance is a useful step to take just before you are set to distribute the seed. It helps the seed penetrate the soil more rapidly and protect it from being washed elsewhere by rain, and from browsing wildlife (birds love seed!).
Raking: this is a great method for restoration projects in woodlands, forest floors, sloped locations and small areas being seeded. Hand raking disturbs the ground enough to allow seed to get into the soil, but doesn’t disturb soil structure or existing native plants as much as more intensive ground disturbance. It also allows you to easily avoid any preexisting native plants that you are trying to protect.
Light tillage: you can also use a small tiller / cultivator to prepare an area for seeding. This is particularly useful in pasture and farmland. If you have a weed issues, this is a method that should be considered carefully, as ground disturbance can expose weed seed banks in the soil to the ideal conditions for growth.
Keep an eye out for our next blog post about best practices in native plant seeding for your ecological restoration project! Don’t forget that we are always updating the Rogue Native Plant Partnership Resources Library with new useful resources for ecological restoration projects – from backyards to woodlands and everything in between!