Have you ever wondered what a lot of rain might do to all that acreage burned in the fires? You’re not the only one. In fact, many scientists have actually studied it.
With experts still predicting an El Niño like that of 1997, we could be in for some fairly significant erosion.
El Niño is defined by the National Oceanic and Atmospheric Administration (NOAA) as “a disruption of the ocean-atmosphere system in the tropical pacific having important consequences for weather and climate around the globe.” That’s a mouth full of a definition, but what it means to us is an above normal amount of rain this year.
When land no longer has the stabilizing power of vegetation, it sheds water, which picks up soil, ash and debris and takes it downhill, causing erosion, debris flows and flooding. How much and to what degree these might occur depends on the extent of the burn, the amount of rainfall, and the topography of where you live. Lake County is mountainous and we have some pretty badly burned areas.
By washing away the topsoil, erosion robs the land of its ability to grow trees and shrubs. It steals nutrients that provide for healthy plants and it loots the land’s potential to reestablish vegetation. In addition, eroding soil carries silt into streams and lakes, degrading water quality and aquatic habitat.
Techniques to prevent or diminish erosion include covering the soil and diverting or intercepting water flows. Practical soil covering techniques for most homeowners are re-seeding or mulching.
A great form of erosion control is through vegetation. It’s nature’s way. The roots grow deeply into soil, anchoring it in place. When it rains, the vegetation also slows the speed of water flowing downhill.
Mulching is also nature’s way of erosion control. Leaves, sticks and vegetative detritus fall to the forest floor, creating “litter.” Forest litter is nature’s mulch. As leaves fall, they become incorporated into the soil, creating a bond, which holds the cover in place. This organic layer prevents splash erosion from raindrops and also slows the overland water
Seeding
To consider if seeding is the right choice for you, walk around your property. Since there may be places where native seed survived the fire, it may not be necessary or even counterproductive, creating competition for the native seeds present. Here is how you tell, whether or not you need to seed:
Look for white ash. White ash means the fire got so hot that it likely destroyed the native seeds. You’ll find these places where there was thick, heavy brush that gave more fuel for an intense fire. These areas will need seeding.
Look for slope. Are you on a flat spot or downhill? Is the slope steep or mild? The steeper the slope, the more erosion potential, and even if there is seed left, it will likely get washed downhill, because there is nothing to hold it in place.
Check for hydrophobic soils. These are areas where burning of the forest litter has actually changed the chemical composition of the soil, making it waxy. In turn when water won’t soak into the ground, it becomes difficult for vegetation to reestablish. The way you tell is to pour a little water on the ground and watch it. If it forms a little ball that doesn’t soak in for at least 10 seconds, your soil is moderately hydrophobic. If it doesn’t soak in for more than 40 seconds, your soil is strongly hydrophobic. Either way you’ll need to treat the soil. On gentle slopes you’ll need to break up the soil with a shovel or rake to allow water to penetrate. On steep slopes you’ll need to spray a soil surfactant.
A soil surfactant is a chemical that reacts with the hydrophobic soil layer and breaks it up, so water can penetrate it. For a great discussion about soil surfactants, visit http://oregonstate.edu/dept/eoarc/sites/default/files/publication/791.pdf.
If you live on a relatively flat spot without hydrophobic soils, you may only need to seed. As land denuded by fire can leave it susceptible to invasive weeds, we recommend using a native seed mixture. Broadcast the seed using a hand or mechanical spreader. For a detailed discussion on types of seeds, rates of application and spreading techniques check out http://www.eldoradorcd.org/nodes/info/documents/Post_Fire/2013%20Reseeding%20burnded%20areas%20for%20Homeowners.pdf.
If you have a mild slope you may need to mulch in addition to seeding, but if you have a steep slope, like 3:1, you definitely need to mulch.
Mulching
Mulching is covering the soil, whether it is with an organic, non-organic or synthetic material. Which one you choose, depends on several factors, including cost, topography, acreage and use of land.
An economical choice for mulching is called slash spreading. Slash is a term used in the forest industry to describe the stems and branches left over after logging operations. In that vein, any unburned tree materials, branches or stumps can be chipped and spread as mulch. These may be hard to find in some burned areas but you might know someone who wouldn’t mind help with yard cleanup in exchange for them.
Slash spreading is a lot of work, and if you don’t have the time, there are fairly inexpensive materials commonly used for mulching. They include straw, wood chips and shredded bark.
Moving up the price scale, other products commonly used on steep slopes are jute mats, netting and inorganic mulches such as gravel, crushed granite or larger stones, such as “Rip Rap” for use on 2:1 slopes.
For a great description on mulches including when, where, best uses for materials and application methods, EPA’s Best Management Practices has detailed information in its brochure located at the following website: http://www2.epa.gov/national-pollutant-discharge-elimination-system-npdes/national-menu-best-management-practices-bmps#edu.
Diversion and interception techniques
Since slopes that are 2:1 or greater have poor potential to re-vegetate, diverting or intercepting rainfall can be an effective way to decrease erosion. Intercepting and diverting structures help slow the speed of water, or channel it away from areas like your house, an inlet drain, or a creek. Listed below are several erosion control methods commonly used in the construction industry or by the U.S. Forest Service. However, be aware that there may be legal consequences if you divert water from your land onto a neighboring property, increasing their erosion or flooding potential.
Contour felling is an intercepting method where trees are cut (those already dead from the fire), positioned perpendicular to the contour of the land in a brick-like pattern and anchored in place, so that they intercept and decrease the speed of water flowing down the hill.
Water bars are a diversion technique to prevent erosion on roads, trails or paths. A dirt berm is constructed diagonally across the road or trail, directing water to flow over the side of the hill. A depression is dug on the uphill side of the berm to collect sediment.
Silt fences are temporary sediment barriers. The sediment backs up behind the fence, which prevents it from washing into undesirable areas. They can be made from woven, non-woven and monofilament materials purchased at hardware stores. These are not permanent features and are meant only to provide erosion protection until other soil stabilization methods take place, such as re-vegetation.
For more details on the proper construction, placement and appropriate materials for installing these structures, take a look at the following websites, which are also great places for more information on the topic:
• http://texasforestservice.tamu.edu/uploadedFiles/TFSMain/Manage_Forest_and_Land/Water_Resources_and_BMPs/Stewardship/Best%20Managment%20Practices%20-%20Practice%20Guide%20-%20STATEWIDE%20-%20revision,9-2012.pdf
• http://www3.epa.gov/npdes/pubs/siltfences.pdf
• http://txforestservice.tamu.edu/uploadedFiles/TFSMain/Wildfires_and_Disasters/Fire_Danger/Get_Help_After_the_Fire/Bastrop_Fire_-_Short_Term_BMPs_for_Water_Quality__Technical_Guidance.pdf
For more information, contact the U.C. Master Gardener Program, U.C. Cooperative Extension — Lake County at (707) 263-6838 or email celake@ucanr.edu.
Visit the office at The Agricultural Center: 883 Lakeport Blvd. in Lakeport.
Other ways to find out about the program: http://celake.ucdavis.edu/Master_Gardener/www.facebook.com/UCCELakeCountyMasterGardeners.
