The following article was adapted from an article by Patt Wilson McDaniel for the California Native Plant Society.
In the wake of the Thomas Fire, many people have expressed concern over the state of the burn areas, particularly in relation to landslides from the bare slopes and how native and invasive plants will respond.
Botanists, ecologists, and other professionals have been researching and discussing this topic for more than 50 years. In the past, agencies would rush to spread non-native seeds along burnt hillsides to prevent runoff and erosion, but as our understanding of fire ecology has grown we have come to learn that these practices are unnecessary and sometimes even counter-productive.
We learned the hard way that seeding with non-natives (most often ryegrass) caused more problems than it solved. On the surface, it appeared that ryegrass would grow rapidly despite little water and stabilize the hillsides. Yet after agencies called it a success and moved on to the next project it would later dry out when the rainy season declined, resulting in greater fuel for fires and providing less stability in the soil than the native perennial bunchgrasses would have. We have since learned that the native grasses that ryegrass would displace actually send down deep roots very quickly, and the resulting plant was more stable and more resistant to drought. Yet seeding even with natives is not often a good approach for preventing erosion simply because it is redundant: most natural areas already have a substantial seed bank with a variety of local species that respond quickly to fire.
Our understanding of how our local ecosystems respond to fire has grown over the years. When fire clears dense, old-growth chaparral, space opens up and seed banks that have been waiting for many years to be stimulated by fire, flourish and dormant root systems sprout anew. Many seeds need to be charred by fire to break the outer coating or change its chemical composition and allow the seed to germinate. Other plants have large root systems that retain nutrients and energy and are able to 'stump sprout' after a fire. The combination of a variety of annual and perennial plants growing from seed and the regrowth of shrubs from stumps results in a complex interweaving of different root types that can stabilize the soil better than any artificial seeding mix that could be devised. Our local vegetation has evolved with occasional fires and many of the local species have evolved adaptation methods to survive fires and remain dormant for years between fires. Therefore counter-intuitive as it may be, the most effective approach is to let nature take its course, watch for and remove invasive species, and take measures to control runoff and erosion if necessary.
From Betsey Landis, Los Angeles Santa Monica Mountains Chapter CNPS: ". . . the recovery in healthy habitat comes in a cascade of immediate germination from seedbanks, root sprouts, and stump sprouts. Species such as wild cucumber and morning glory vines immediately spread out vines to cover the ground to prevent erosion. Bunch grasses re-sprout. Bay laurel puts out fresh sprouts very fast, big pod Ceanothus germinates very quickly, as do some Prunus, while spiny Ceanothus prefers to stump sprout, as do toyon, and some Arctostaphylos. Of course, there are the fire-followers who are there quickly to stabilize the soil and provide food and shelter for the animals. Malosma laurina is very interesting because it stump-sprouts quickly, puts out new growth fast and is one of the first to bloom and provide berries for birds and animals to eat. The grasses produce seeds; the fire followers bloom and provide pollen and nectar. The chaparral community is truly a community, with many different species phasing in their recovery so the ecosystem can survive. It seems to take about five years to reach a point where all the main plants are again able to produce fairly healthy (viable) seeds and fruit. No one should add seeds or new plants until the severity of the fire damage is known. For instance, all trees are burned past their root collars, large bunch grasses are burned down into the ground, and rodent tunnels are collapsed or filled with char. One really needs to wait until there is some rain to see what comes up."
Flooding and landslides remain a chief concern post-fire and the determining factor in their severity is the nature of rain we receive. If we get gentle and intermittent rains, the water will soak into the soil and the plants will grow and provide the protection we need from future rains. If the rains come hard and heavy, no amount of seeding could have prevented runoff. The only effective way to prevent landslides and flooding on bare hillsides is with physical barriers such as matting or erosion control waddles. For those that are concerned about flooding and landslides near their homes, there are a couple things you can do:
Our recommendation is to use biodegradable matting (like coconut fiber) with a wide weave so plants can sprout through it. Farm supply stores and hardware stores carry it, although a lot of people will be trying to buy it after a fire and it may need to be ordered. The matting should be placed on steep, bare slopes and held in place with fabric staples which are also sold with the matting. On very steep slopes the fabric can be rolled into 'wattles' and held in place with wooden stakes to make check dams.
Be very careful when choosing the material to use for erosion control matting. As mentioned above, using biodegradable materials such as coconut fiber is a good idea because it is temporary and biodegradable. Alternatively, there are a number of types of plastic mats that are meant to stay in place and not degrade. Depending on the slope profile and conditions, the benefits of leaving the plastic mesh in place may outweigh the costs.
Also, if you decide to use the premade wattles we strongly encourage you to do your research on the filling of the wattle as they are made from a vast variety of materials and they can introduce weeds into native habitat. When considering your options for erosion control methods and materials, make sure you know your specific goals of the areas targeted for erosion control and pick the products that will work best for each area. Depending on the conditions, contours and overall goals of your specific restoration sites erosion control materials may not be necessary. The spreading of locally sourced seed and possibly the installation of vegetative cuttings/container stock may all that is needed. Of course, the plant palette would be as site-specific as possible and could transition between multiple zones such as riparian, chaparral, etc.
We would happily provide free advice or consultation if your home has been impacted by the Thomas Fire. Get in touch with us by emailing firstname.lastname@example.org